For body kits - I think the front stock bumper is still the best looking thing, but here are some alternatives:
www.fxdesigns.com
www.importfan.com
www.erebuni.com
Look for the kits for Ford Probe. Personally, I like the CW front end and the Sinsei front end - however, both of those bumpers require extensive body work to make fit properly and not fall off. They are both fiberglass and not the best quality.
For sideskirts, my personal favorites are the fxdesigns sideskirts.
Rear bumpers - I like the Sinsei rear, but again it needs a LOT of work to make fit (4-10 hours of shop work @ $60/hr...). I also like the FXDesigns prototype rear end.
From these 3, FXDesigns makes the highest quality work. Erebuni is second, with Sinsei/CW quality being very bad...