Wacom is the only brand to look at. There are other cheaper brands out there, and I am sure there are happy users of some of them, but all I have heard about them are complaints.

The best value on the market right now, in my opinion, is the Wacom Bamboo Fun. It's affordable and has all of the features a casual user is likely to need. Although the Intuos line is certainly superior, only a very skilled user is likely to notice the difference in pressure sensitivity. All Wacom USB tablets have drivers for Mac and Windows going back to Win98, but you may need to visit the Wacom website to download the ones you need, since apparently they've stopped shipping drivers for older operating systems in the box. There are even Linux drivers, although I understand that it's a bit of a chore to get them to work. But Linux users are quite used to that.