Sculptris is currently a free to use 3d sculpting program (currently in Alpha stage). It is slightly more basic and raw compared to the big sculpting tools (mudbox/Zbrush) but it still has a great charm and excellent ease of use.
Here are a few tests done with it (using the default sphere as the starting point).
Below: A goblin
I found the program really easy to use and a nice start for those not used to importing objects in to Maya for a render. (I used a modified version of MayaSSS Fast Skin Shader as a base for the skin with my texture painted colours as bump added to it, then a simple lighting rig for the images). The downside is it's quite a bit harder to get a refined model such as in zbrush and poly count can be quite high (although the reduce brush does an excellent job of lowering poly count).
This program is perfect for lunch time doodles at work or test ideas which can then be developed in more powerful software combinations. Give it a go!