I use a Wacom Intuos2 6x8 at work and a Wacom Intuos 9x12 at home and love them. It's a must have if you're serious about graphics apps.
Tablet PCs are nice, but one thing I was taught in my art classes was that you shouldn't be looking at the paper when you're drawing, you should be looking at your subject. That said, I'm eagerly waiting for Wacom Cintiqs to go down in price.
http://www.wacom.com/productinfo/intuos.cfm
Totally worth the price.