There's a really cool new sculpting program in development called Sculptris. The main advantage over Blender's built-in sculpting tools is the automatic tesselation, so that more details are added to the mesh only where they are really needed. I guess that's one reason why Sculptris is so fast compared to Blender. Adding arms and legs to a model is also very easy because of this tesselation.
http://www.sculptris.com/
http://www.drpetter.se/project_sculpt.html
I made a ugly, little, crawling monster for testing purposes (I hope you're disgusted ) and a human head which I modelled in about 15 min without reference (it still needs some work):