My wife is using a Genius Pensketch 12x9 tablet with inkscape and gimp. It's far more affordable than a wacom with similar specifications (resolution, pressure levels, etc). It only lacks the tilt function and the eraser in the pen, but if you're looking for a large tablet for a fraction of the price of a Wacom, imo this is a great choice. It works under linux (not out of the box, but there is a step-by-step tutorial in Ubuntu Forums).
You can see what she's doing with that tablet in www.flickr.com/photos/superdd
Oh, and btw, someone asked about Cintiq support under linux. Jimmac just bought one and got it to work under linux without problems (there's an installing guide in his blog). Those things are great, but wow, they aren't cheap. :-)