i recently bought
http://www.trust.com/products/product.aspx?artnr=12579
this one
of course its nothing in compare to wacom but its very very cheap and it wouldnt do the job better if i had a wacom.
It has a good responsive time and a good resolution.
the only negative thing is that the pen works with battery
but it lasts very long i havent change it since i bought it and its been about a month and a half.
The tablet zach mentioned is amazing i used one of them at work (i left)
and its pretty cool especially when you use it with corel painter.