I have a Wacom Graphite 4x6 tablet. It is small as heck, but it gets the job done. I would love one of those huge ones, but they are like $700+. I spent about $100 for mine about 2 years ago. You can find some of cheaper tablets out there, but you do get what you pay for. I had one before this called "Pablo" that completly sucked. The pen was wired to the tablet and there was hardly any pressure sentivity. 
If you want something just to play around with, Get a Wacom Graphite2. They will run around $100. I use mine just about everday for graphic design in Adobe Ilustrator 9.