you could prob find a wacom intuos 3 used for a decent price.
The intuos 4 is the newest and shiniest. But you could find a intuous 3 for a deal. I would stay away from the bamboo series.
Have you ever used a tablet before? Some people prefer large or some like small. I recommend a size in the middle because when you have to reach the corners on the larger sized tablets and can be somewhat daunting, and when using one that is to small you feel like you want a little more.