Velo Girls has had a booth there in the past. Lots of vendors (clubs, industry, etc). Lots of used stuff and a bit of new stuff too. Go early to get the best stuff (lots of dealing goes on during set-up on Friday).
Velo Swap used to be at the Cow Palace (with lots of parking). Since moving it to SF (with no parking), attendance and participation by vendors has gone down. Even though it's convenient to public transportation, it's hard to carry a bike on BART if you rode your bike to the swap!!!