I used a Wacom Bamboo for several years, but it finally died. I just replaced it with
an Wacom Intuos that is approximately the same size. I wouldn't be without a pen tablet,
I use it in Photoshop, but I don't use Illustrator. Wacom is the brand of choice for most.
You need only the smaller tablet with Photoshop. Normally, you're working on a zoomed
in area and the small tablet is perfectly adequate.
If you intend to do free-hand drawing, you'll need a larger tablet.