I have used a variety of sources for repair parts, as I am a notorious "consumer shopper". This link will take you to a page listing a lot of the parts (big and small) that I've replaced. The part numbers may be helpful.
Here is a list of the places I always check out first (listed alphabetically in each section)
Full line of aftermarket & performance parts, accessories, etc
Good selection of commonly replaced parts
Other supply houses
Performance-oriented
And...of course eBay
Automotion (a Performance Products company)
Pelican Parts
Mid America Motorworks (aka Tweeks)
AllEuro
All EurAsian Auto Parts
Carmadillo
EuroWebParts
GermanParts (some hard to find dealership parts)
PAP parts
SpeedyCarParts.com (Formerly known as "ThePartsBin.com")
Stop Shop and Drive
OEM Porsche Parts (9Parts.com)
Coburn Myers (fasteners)
Import Replacement Parts
NAPA Online (seals, bearings)
SpecialTAutomotive (CIS Fuel system)
Andial
EBS Racing
GT-Racing
Integral Cams
Paragon Products
SI Valves