1) PPaint for pixel art
Slightly more convenient than DPaint (although this one is better for animations, but that's my brother's department)
2) DOpus, for the usual file management. Never seen Dirwork before :| I might as well give that one a try...
3) And Maxon for 3D mockups and similar fiddling. The one and only 3D rendering program I figured out on myself without any manual
