I've got a Wacom Intuos A4 tablet, which I love. I haven't been using it anywhere near enough due to workspace issues, but now I have my new iMac I find myself with a lot more desk space, so I'm planning to use it a lot more. I especially enjoy the zoom slider and function buttons on my particular model that helps to iradicate the need for the mouse when you are using it.
I tend to use the tablet for illustrative work and it's perfect to do anything in photoshop. If you are used to hand drawn conceptualising this is a wonderfully intuative tool that can easily transfer those scribbled doodles onto the screen without cleaning it up too much.
Only drawback is that this particular tablet was expensive. But I find that it is worth it for the seemingly huge A4 drawing area.