Wings 3D Development Forum

One of the methods currently in use is "create the highres model first - inside the sculpt software and then after done with the highres you create a lowpoly shell on top of the highres one and uvw map that, and then later proceed to xnormal". (ref. post)

Softwares
Sculptris (alpha 6 - the last and unique version after Pixologic has "bought" the freeware Sculptris).
Sculptris cheat sheet by 3dioot and a HTML version by rbtyod

xNormal (freeware): It is an application to generate normal / ambient occlusion / displacement maps.
It can also project the texture of the highpoly model into the lowpoly mesh (complete texture transfer, even with different topologies).

Tips / Tutorials
Re-Topologize a Game-Ready Alien Head in Blender by Jonathan Williamson

Softwares
MeshLab
Tattoo 3D Texturing
It's a small application for paint texture. It's not sophisticate, but is useful and free (for non commercial use).
I think it would be a good tool for painting textures of low/medium polys objects. They need be UVMapped before load into the software.
Check the help to know about the shortcuts.

Tip / Tutorial
Polygon Reduction with Meshlab on Shapeways site