I've used Wacom tablets for years, and they are good, but expensive and haven't evolved much over the years.
An artist (Ray Frenden) has reviewed a range of graphics tablets available, and has a couple of newer, MUCH less expensive options that are competitive with Wacom.
I'd say the best starter tablet he's reviewed seem to be the $50 Monoprice 10"x6.25" or the $90 Monoprice 12"x9"
I haven't used these yet. I can't personally vouch for them, but Ray is very hardcore about this stuff... so I trust his opinion.
This biggest issue with these over the wacom tablets is that the Monoprice pens need batteries... but you save so much $, it may be a worthwhile hassle.