Yeah, I'd pretty much agree with everyting mentioned so far, especially;
Audacity, for editing the sounds/music I've used in my game.
Paint.net, for converting images to DDs format.
Gimp, for all other texture/image creation.
VLC Media, for music and movie file playback.
7Zip, for archiving files.
Blender, finally found a decent tutorial to learn it, once I've mastered Milkshape!
And not forgetting the main ones I use all the time;
Mozilla Firefox and Thunderbird, for web browsing and emails.
Ubuntu Linux, no explanation necessary!!!