The affordable option is the wacom bamboo.
If you want more, then the graphire, the next level would be an intuos, ignore the others (the one where you draw on the screen, clitiq(?)) unless you are really committed and want to use it in a professional manner, otherwise its a waste of money for a hobbiest.
Start with the bamboo first, otherwise you are just wasting alot of money. Intuos is more of a professional sort but one of the most expensive :/
Bamboo I think has 256-512 levels of pressure (making it smoother for pressure and opacity transition).
Graphire (at least mine which is graphire 4) is 512.
The Intuos has 1024 levels of pressure.
My graphire 4 (6x8 inch) was 160 AUD second hand from a professor in germany about 3 years ago, I got it from ebay.
I helped anarch get the same type as me, but cheaper, around 100AUD. IF you want it new, expect about $200+ (same model).
But bamboos are cheap and affordable for the hobbiest, freelancer or student. Here they are around 50-80AUD for the 4x5inch? size. Around 100-200 AUD for the 6x8inch.
For beginners I suggest a 4x5 or such size or a 6x8. Ones that are like..what? 9x12? or so... they are not really practical anymore as they become a pain to use as they take up too much desk space and have to be on your lap or knees when you use them. Bigger is never better, nor is tiny/small.
Go to your computer store, find some bamboos and ask to see them in person and hold on and judge the size yourself and see if you think its the one for you.