I totally forgot to publish this last night... Anyway, here it is. Sorry if it's a little rough.

I figured that there was one more thing missing from the game production tools I'd posted - sound! So, I've tried to find parallel sets of sound design tools. The problem is that I don't know much about sound tools, so I've just put this list together based on tools that I've had a play with. I've used these tools to either generate sounds, record new sounds, or modify existing sounds. I've honestly not played with the third program much at all, and can't say much about it...

So, here's the list:

Audacity
This is a great open source sound recording and editing tool. With a ton of custom filters, and the ability to create your own, there isn't much missing from this program. If you've ever looked for an open source sound program before, you've likely come across Audacity. It's fairly simple to install and get going with, and allows you to output files to a variety of formats. If you are recording your own sounds, there are some filters and effects that can help you clean up the sounds to improve quality etc.

Sfxr
This is a fun and simple tool designed to generate sweet, sweet 8-bit sounds. With a bunch of different mutators for the sounds, and some preset constraints for randomly generated sounds - explosions, jumps, etc. - this program is fun just to play with generating beeps and boops.
You can save files out to wav format.

Musagi
I've never actually created anything I'd actually use with Musagi before, but I've heard some great stuff composed with it. It's pretty buggy, but mostly you can work with it. Incidentally, Sfxr and Musagi are created by the same designer - DrPetter