Here's a few:
www.wingswest.com (about the only urethane kit out there. good quality, not too aggressive, but most people have this kit).
www.visracing.com
www.erebuni.com
There's a bunch of links on
www.4thgenerationcivic.com for body kits and whatnot. Also check out the thread at the top of the forum about "best 4th gen sites"...
Hope that helps.