Since every now and then there seems to be a new member on the boards asking questions on a certain body kit, I figured making a comprehensive list of where to get different body kits from would be useful. I've added a couple to start with. Anyone else willing to donate useful information just post here, and I'll update this post
Fitment
Fitment is posted in stars: a "* * * * *" means it's a very good fitting body kit (meaning no modification needed to make the body kit fit) while a "*" means it's very low quality. On another note, a "^" is half of a star. These ratings do not include prep work (to make the paint stick better, etc.) which most if not all bodykits require. (Thanks to Beto for correcting me on this

) Feel free to correct me if I list something wrong
Fitment Ratings:
* * * * * (
5)
Perfect fitment. Speaks for itself.
* * * * ^ (
4.5)
Excellent fitment. Very little modification may be required for a good fit. You shouldn't have to worry too much about these, neither. Most body kits of this rating will likely not need anything to be modified, although sometimes you may run into one that will require small modification.
* * * * (
4)
Great fitment. Little modification required for a good fit. Still not a big concern here, although very small modification will likely be required.
* * * ^ (
3.5)
Average fitment. Slightly above average, these are bodykits that may come with some small fitment problems which will require modification (sanding, etc.) to get a good fit out of.
* * * (
3)
Average fitment. These are decent fitting body kits, but will not be flawless. After some modification which will likely be required, will still have good fitment. Very small misalignments may be noticed after installation.
* * ^ (2.5)
Fair fitment. These are below recommended fitting quality. Will not be flawless, and will probly need moderate modification to have a decent/good fit. Some fitting problems may occur and may be seen after installation is complete.
* * (2)
Poor fitment. These are below recommended fitting quality. Will more than likely have problems, including air bubbles (if the kit is urethane), some warps and/or lumpy areas. Fitting problems are likely to occur, even after heavy or moderate modification. Fitting problems are almost always present in these body kits.
* ^ (
1.5)
Very poor fitment. These are far below recommended fitting quality. WILL have problems, including large air bubbles (urethane only), scratches, dents, warps, unsmooth edges, and lumpy areas. Heavy modification is iminent, and will likely be required for a decent fit. Not recommended.
* (
1)
Horrible fitment. This is the worst rating. Welcome to the twilight zone. Teh sukk. You can get no worse than this, in fact you should probly just throw this junk away.
Composition
Another thing to note is that Fiberglass is generally less durable than Urethane, but is also lighter, and sometimes much lighter. Some companies use methods to make fiberglass much stronger when creating fiberglass body kits. For example, Veilside uses a gel combination with their fiberglass so in the case of small collisions, it can flex to an even greater degree rather than crack, and cracks aren't a good thing.
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TRD (action package)
Composition: Urethane
Fitment: * * * * * (
5)
Dealers: www.trdtoyota.com
www.wctoyotasport.com
http://www.etoyotas.com
www.trdperformance.com
Replica dealers: http://www.afsmotorsports.com/
Pictures:
http://www.toyota.com/html/shop/vehicles/celica/exterior/celica_exterior.html
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TRD (Elegant package)
Composition: Urethane
Fitment: * * * * * (5)
Dealers: www.trdtoyota.com
www.wctoyotasport.com
http://www.etoyotas.com
Replica dealers: http://www.afsmotorsports.com/
Special Notes: Not listed on dealers' websites. Calling by phone may be required to order.
Pictures: http://www.everythingcelica.com/gal2/exterior2/TRDElegantKit , http://www.everythingcelica.com/gal2/exterior2/TRDElegantBodykitRed1 , http://www.everythingcelica.com/gal2/exterior2/TRDElegantBodykitRed2
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Veilside
Composition: Fiberglass / Gel
Fitment: * * * * * (5)
Quality: * * * * ^ (4.5)
Dealers:http://www.mvpmotorsports.com
www.suprastore.com
Replica dealers: http://www.afsmotorsports.com/
Pictures:
http://www.veilside.com/veilsideusa/aero/toyo/celica.html#
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AFS Motor Sports
Offers various replicas of popular body kits. Quality is excellent for being replicas. Two complaints (including one which was not related to bodykits) , but were taken care of immediately. Superior customer service and low prices. These guys defy the saying "you get what you pay for"
Composition: Fiberglass?
Quality: * * * * ^ (4.5)
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Kaminari
Composition: Urethane or Fiberglass (hand laid 7 layers)
Fitment (Urethane): * * * * ^ (4.5)
Fitment (Fiberglass): * * * * (4)
Dealers: http://www.mbautosports.com (warning: poor customer service, but low price. Some say service is improving.), http://www.kaminari.com (duh) , http://www.conceptautocreations.com/
Pictures:
<a href="http://www.kaminari.com/products/00Celica.htm#big_picture"><img src="http://www.kaminari.com/images_product/00Celica1_sm.jpg" Border=0></a>
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Wings West Lip Kit
Composition: Urethane
Fitment: * * * * ^ (4.5)
Dealers: www.newwayautosports.com
www.trdperformance.com
www.suprastore.com
Special Notes: This kit does NOT fit '03+ Celicas, due to a different stock bumper than previous years of the 7th gen.
Pictures:
http://www.wingswest.com/products_detail.asp?page=1&id=644
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http://www.trial.co.jp/trial-usa/index.htm>Trial[/url
Composition: Fiberglass?
Fitment: * * * * * (5)
Dealers: [url]http://www.i-m-racing.com/trialcel00bo.html
www.suprastore.com
Pictures: http://www.i-m-racing.com/trialcel00bo.html , http://store5.yimg.com/I/supra_1727_48753256
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Black Widow wide bodykit
Composition: Fiberglass
Fitment: * * * * (4)~ * * * * * (5)
Dealers: Feel free to post good dealers
Special Notes: Fitment quality is estimated, and may not be accurate, but should be around the listed area.
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C-One
Composition: Fiber Reinforced Plastic (FRP)
Fitment: * * * * * (5)
Dealers: www.ipnmotorsports.com
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Brash Boy (Fangs)
Composition: Fiberglass?
Fitment: ???
Dealers: ???
Special Notes: May have to be imported from Japan, so expect to spend $$$ on that.
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Team Jetspeed
Fitment: Fiberglass
Quality: ???
Dealers: Look at link
Special Notes: This company is located in Australia, so you will be forced to import it.
Pictures:
[img="http://www.imagestation.com/picture/sraid59/p626b8c27417d082ef70ab6a06c663360/fc57b12c.jpg]
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[url =http://www.bomexaero.com/bomexusa.html]Bomex[/url]
Composition: Fiberglass
Fitment: * * * * * (5)
Dealers: www.mbautosport.com
Pictures:
[IMG=http://www.imagestation.com/picture/sraid59/p0e676e2285cb80db5916b3f7f896af29/fc57b12b.jpg]
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Octane
Composition: Fiberglass
Fitment: * * * ^ (3.5)
Quality: * * * * (4)
Dealers: www.mbautosport.com , www.procarparts.com
Special Notes: The Fitment and Quality may differ depending on where it's purchased from, since some dealers create their own Octane body kits.
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Rod Millen
Composition: Urethane
Fitment: * * * * * (5)
Dealers: http://www.rodmillenstore.com , http://www.mvpmotorsports.com
Special Notes: Link has been corrected, and now leads to the Rod Millen's store instead.
Pictures:
[a href=http://www.mvpmotorsports.com/Merchant/rmm_cel_5pcbody.jpg][IMG=http://www.imagestation.com/picture/sraid59/pf1c788e8f6f8d0c49b30c3cd10d3080b/fc57c9e9.jpg]
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<a href="http://www.mollydesigns.com">Molly Designs</a>
Composition: Urethane
Fitment: * * * * * (<font color="blue">5</font>)
Dealers: www.mollydesigns.com
www.wctoyotasport.com
Pictures: <a href="http://members.shaw.ca/celica.girl/index.html/celica/molly7.jpg">1</a>,<a href="http://members.shaw.ca/celica.girl/index.html/celica/molly5.jpg">2</a>,<a href="http://members.shaw.ca/celica.girl/index.html/celica/mollyrear.jpg">3</a>
Molly Kit Wing Pictures:
http://members.shaw.ca/celica.girl/...lica/molly7.jpg
http://members.shaw.ca/celica.girl/...lica/molly5.jpg
http://members.shaw.ca/celica.girl/...a/mollyrear.jpg
Special Notes:Photos and information courtesy of Celica girl
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Buddy Club
Composition: Varies among dealers
Fitment: Varies among dealers
Dealers: www.afsmotorsports.com , www.mbautosport.com
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Buddy Club 2
Composition: Fiberglass
Fitment: Varies among dealers
Dealers: www.henshinauto.com
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Blitz
Composition: Varies among dealers
Fitment: Varies among dealers
Dealers: www.afsmotorsports.com , www.mbautosport.com
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<a href="http://aprperformance.com">APR300GT widebody kit</a>
Composition: Fiberglass
Fitment: * * * * * (<font color="blue">5</font>)
Dealers: Look under Dealer Locator, found at APR's website (above link)
Pictures: http://aprperformance.com/whatsnew_2003_gt300.htm
Special Notes: Big thanks to BiZzyCeLiGT for help with this one, as well as lots of other bodykits 
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Invader
Composition: Fiberglass
Fitment: Varies among dealers
Dealers: www.mbautosport.com
Special Notes: Known as Invader 6 @ mbautosport.com
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C-West
Composition: Fiberglass
Fitment: * * (<font color="orange">2</font>)
Dealers: www.importfan.com
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JSP "Rave"
Composition: Fiberglass
Fitment: * ^ (<font color="red">1.5</font>)
Dealers: ???
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<a href="http://www.visracing.com">VIS racing's Buddy club replica.</a>
Composition: Fiber Reinforced Plastic
Fitment: * * *(<font color="gold">3</font>)
Quality: * * *(<font color="gold">3</font>)
Dealers: See above link
Special Notes: Information courtesy of satoshi
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<a href="http://www.tte.de">TTE lip spoiler and sideskirts</a>
Composition: Urethane
Fitment: * * * * * (<font color="blue">5</font>)
Quality: * * * * * (<font color="blue">5</font>)
Dealers: ???
Pictures: http://www.tte-saj.com/img/am27759.gif (lip spoiler)
Special Notes: Side skirts not shown on above web site. Information courtesy of satoshi, corrections by Dimitri
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VARIS (Extremor)
Composition:FRP
Fitment: * * * * * (<font color="blue">5</font>)
Quality: * * * * ^ (<font color="green">4.5</font>)
Dealers: ???
Pictures: http://www.varis.co.jp/zzt23a1.jpg
Special Notes: Information courtesy of satoshi
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K5 Kit (replica)
Composition: Fiberglass
Fitment: * * * ^ (<font color="gold">3.5</font>)
Quality: * * * *(<font color="green">4</font>)
Replica dealers: http://www.extremedimensions.com/shopexd.asp?id=2109
Pictures: http://www.everythingcelica.com/gal...ring=K2+BODYKIT, http://www.redlineautosport.com/gal...ame=sibalcelica
Special Notes: Information courtesy of celicaGT
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I know I'm missing A LOT of information, but hopefully some of you will contribute info to help out 
Credits go out to WRENCHHEAD, GT-Skid, Black Halo, coOOlcelica, QWKsilvr808, JT$, Celica girl, BiZzyCeLiGT, Pure Racer, 00 scrub, Mistrimeat, PhatCellyGT, TRD-GT (Beto), 2KFLCELLY, satoshi, celicaGT, Dimitri for contributing information 