Wacom Intuos, preferably 6x8.  6x8 gives enough room for fine detail, but
isn't so big that your hand movements have to be exaggerated.
Remember...the tablet surface itself represents your screen...not merely
movement, like a mouse.  If you move your pen to the upper right corner of
the tablet...you'll be pointing to the upper right corner of your screen.
With the Intuos line of Wacom tablets, you can also specify a portion of the
screen to be represented by the tablet...for times when you want even
greater motion control.

While Wacom's cheaper Graphire often comes with a mouse, the tablet itself
isn't as sensitive as the Intuos.
You'll be hard-pressed to do better than Wacom for mainstream tablets.

Mark²

No-one ever got fired for buying Wacom.  Graphire is a Wacom item.

As others have said, Wacom is the only game in town. It just depends on
your usage and budget as to which model you prefer. I've used the 4"x5"
Graphire for years, and I haven't run into any problems at all with the
size. I do like the Intuos' improved sensitivity, but for most photo
retouching it hasn't been a problem for me. If I had money to burn (and
wasn't burning it on other photo & lighting equip) I would get an Intuos
6"x8".

Randy.