Personally, I use
Audacity for recording/mixing, and
Hydrogen for drums - but both of these have already been mentioned.
The only significant program I use that I haven't seen spoken about here is the brilliant
Psycle. It's an open-source tracker/sequencer with full VST2 support - and I swear by it.
http://sourceforge.net/projects/psycle/ <- Check it out and see what you think.
