OK, I guess I didn't understand what you meant when you said "I just want something used that I can hook up to my laptop". The USB gps'es I mentioned are just little gadgets that plug into a laptop. You use them with software running on the laptop to show your position. By themselves, they don't do anything and they don't have any screen.
It sounds like you want a regular handheld GPS that can also be connected to a laptop for downloading caches. That is something I don't do myself, so I can't help much.
The newest Garmin units support something called "paperless geocaching" where all the info you need is stored on the GPS itself. These would include the Oregon, Dakota and Colorado series as well as the Nuvi 500 and 550.