Just thought I would contribute to this list
![Happy :)](./images/smilies/icon_smile.gif)
For those of us who do 3D artwork like myself I find these tools useful
![Happy :)](./images/smilies/icon_smile.gif)
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