I use a Wacom Intuos3 9 x 12 inch usb tablet, and I love it. I also had a Calcomp tablet previously to this one. Calcomp no longer makes drawing tablets as far as I know.
It's not great for actually moving sliders for white balance, exposure, black levels and that sort of thing and for Lightroom it's not that great.
It is superb for retouching though.The tablet will shine any time you have to change a raster image at the pixel level. Once you try removing backscatter with the pen on a tablet, you will never want to go back to using a mouse.
Wacom is the market leader in this segment. The only thing better, is to step up to one of their Cintiq displays. With these Cintiq displays, you actually see the image under your pen, so hand - eye co-ordination is second to none. Hand - eye co-ordination with the regular Intuos tablet is easy to adjust to as well.
Each Wacom tablet comes with a pen or stylus, a mouse, and function strips on the sides of the tablet.
But it gets better.
By using the accompanying software that comes with the tablet, you can customize all your Wacom mouse clicks, pen clicks and tablet function bar buttons as well. This may not sound that great, all and by itself but, I have set mine up so that I can access all my retouching tools without ever having to reach for the keyboard to change tools. Works in Photoshop and Corel Painter as well.
Hope this helps.
Feel free to PM me if you do decide to buy and you need help setting up the custom mouse clicks.