DrivewireThis site has some of the most reasonable prices I have come across for most of the less pricey type parts. Paul's site is a great resource (and the diagrams linked to the porsche part numbers is awesome.) I usually start there to get some good ball park prices and then I cross reference to Drivewire. Most often the Drivewire site will beat it by a good margin and shipping on orders over $50 is free!
For example, a clutch disk at GPR, Pelican and others was hovering in the $125 range. Drivewire had it for $63 and it was at my door in 2 days (but I'm probably only 100 miles from them.)
I haven't had to return anything yet, or try to ask anyone for advice so I can't vouch for customer service. Pelican and GPR seem to excell in that area. My experience with Auto Atlanta have been less than stellar and I feel they are overpriced and not as honest about what they represent.
My $.02