best place to buy aftermarket parts

the mods should make a sticky on where the best place to buy after market performance parts are.

E-bay; you can find most things there cheaper than on most sites. It may seem like an obvious answer to most (ie. maybe not the answer you're looking for); but whenever I've looked up parts I can pretty much find anything I want on there instead of a slightly or highly limited selection of products. Just my 2¢.

www.groupbuycenter.com

Now how exactly does that group buy thing work?