Personally I wouldn't 100% trust eBay for getting a tablet, as sometimes (not all the time!) little things can be missing or broken and it's REALLY hard to get a refund or the like. Unless, you know, the seller's got a ton of reps and the like. But try not to buy used.
As for what model, Bamboo is probably a good starter model to buy. They're fairly cheap at $100 or so dollars new off the wacom website, and it's really worth it to get a brand new one. It takes some taking used to, of course.
If you got a bit more cash to spend, though, and don't want to bother learning how to size-differenciate the stylus's movements and the mouse's movements, Cintiqs are the best in the business. Be prepared to shell out $1-2K for one though. Regardless, they're for really professional work, as they have a VERY large drawing area (you get a size that matches your screen) and you can watch what you are doing on the actual tablet iirc.
But yeah, Bamboo's probably your best bet. Again, I HIGHLY advise buying anything but new ones.