I've just recently bought a bamboo fun. It's an awesome tablet.
It is a5 size for the sensitive area, but I find that it is all i really need being used to drawing via pencil/pen.
I think the only reason to go bigger is if you are a painter and you're used to making large brush strokes from the elbow rather than wrist. you can get a bamboo bundled with photoshop elements which is pretty sweet.
also check out this thread
http://forum.thegamecreators.com/?m=forum_view&t=192091&b=2
about $220 au for mine. very happy with wacom products
Sometimes I like to use words out of contents