Aircooled.Net You might pay a little more at Aircooled.Net, but you always know what you're getting - quality stuff for your precious aircooled VW. They don't sell junk, and they stand behind what they well. Aircooled.Net's excellent online ordering system also makes it nearly impossible to order the wrong parts for your car.
CIP CIP stocks a lot of Type 3 parts at very reasonable prices. If you know exactly what you're looking for, this is usually the first place to stop when looking for basic parts. They even carry some harder-to-find items like seals, interior parts, and suspension components.
Partsgeek has been selling new, OEM and aftermarket parts and accessories since 2008. They have over 195,000 Volkswagen parts and accessories in stock.
Type 3 Detectives The Type 3 Detectives specialize in finding "unobtainium." If you're looking for that impossible-to-find part for your Type 3, chances are they either have it or can find it. You won't have to come up with a retainer fee, but you might want to have a few Benjamin Franklins (or a couple Parnells) collected together before you call them.
ISP West ISP West sells a lot of NOS stuff on Ebay under the username PIMPPRIDE. As their "Buy It Now" prices are usually also their reserve prices, they're pretty much using Ebay as cheap advertisement. They sell top-notch stuff though, including Type 3 seals and other hard to find parts. Once again, you'll pay a premium for the best stuff.
LN Engineering If you're planning on building the coolest-running, longest-lasting aircooled engine, you definitely want to check out LN Engineering's Nickies and Biral Babies. Hopefully someday I'll be able to afford them. Damn. Lifetime Warranty too!
West Coast Metric West Coast Metric is yet another Vintage VW parts retailer. Their online ordering system is temporarily down, but you can still view the catalog, which contains part numbers and descriptions.