Just thought I would contribute to this list

For those of us who do 3D artwork like myself I find these tools useful

dDo - Texture Creation tool for 3D Models. Requires Photoshop. LINK
Xnormal - Freeware tool for Normal maps, Ambient occlusion maps, etc. Link
General stuff
PureRef - an awesome bit of software for reference organization, viewing and re-sizing. Link