From what I've heard, pen and tablets are a pain to deal with in Maya but if you're doing a lot of work in photoshop or Illustrator (or Freehand) or really anything that supports pressure-sensitive functions, the wacom intuos is a good series. Awesome for painting textures and whatnot. Size depends on what you need....6 x 8 would be good.
"Terminat Bora Diem, Terminal Auctor opus."