http://pixologic.com/zbrush/trial/

Highly recommended if you want to get into modeling, Zbrush is industry standard.

I'm pretty much freaking out about this because they used to have a trial version and then took it down for the longest time. Previously, you would have to pay for the full version which is really expensive or use Sculptris which is free but lack most of the new features (it's the first Zbrush) but hey, now you get 45 days with it.

Zbrush was what I used to sculpt the Dragon Priest Huna:

http://www.bzpower.com/board/topic/18449-dragon-priest-huna/