I myself just bought a Genius MPad or such, 9.5" x 7.5". It's got excellent specs for photoshopping (<2ms response, 1024 pen pressure, 4000lpi widescreen format as I use dual monitors), and is of high quality construction. As a hobbyist here also it does me fine. It cost me only $149.95AUD and beats down on the Bamboo range IMO, however, if you're feeling pro or just love your digiart and have the cash, go the intuos. In this department, you do get what you pay for. Wacom Intuos are the price and quality leader here, but I wouldn't recommend the Wacom Bamboos over the higher spec Genius Pensketches,MPads etc.
Good luck and happy hunting, tablets rule!