I have a Visioneer 5800 USB model that I got a couple years ago for $15 or something and it works great for documents etc. Not so great on photos, but I don't use it for much anyway, and the image quality is pretty good.
I'd recommend any of the new Visioneer models (I think the 5800 is discontinued), because they're REALLY cheap and the quality is pretty good. It hasn't broken like my Umax did in the two years I've used it.