I use a Wacom Intuos3 9" x 12" tablet and I haven't had any problems out of it yet. I think it was between $400-600 but I'm not sure.

I got it for a gift. Any of the Wacom tablets are worth buying though. I know a lot of people who have a Bamboo fun and say those work pretty well and they're cheaper.
I would recommend getting the largest size you can for your money. ^^ The more space you have to draw on, the better, in my opinion.
