I find selling crack to be much more profitable. Helps keep my bitches in line too.
Wait a second... what were we talking about?
Edit: Oh yeah, eBay. I can't sell crack on eBay, but I find that it's easy to find what you're looking for on eBay (pretty much every product on the planet is listed on there somewhere) and then find somewhere on PriceWatch or PriceGrabber that has the same thing for a better price.
Edit: Pricegrabber is no good for crack though, you need to go directly to your local CrackMonkey.