I found the ComputerMusic “CM Studio” program Muzys powerful, but hard to use. Its a “mod tracker”, like skale and OpenMPT.
Though the CM dvds do usually come with a slew of samples, featuring different types every month, like drums, strings, brass, guitar, etc
http://anvilstudio.com/ has a free version, including (at least some) MIDI, but is limited to short time and doesn’t include VST plugin use. Can buy just the plugin functions you want.
Audacity is good for “post processing” sound with multiple tracks, but you need the sound in wav, ogg or mp3 already. Can use some VSTs, not very well though. Mostly use for compositing tracks and editing the wavs.
If you know how to read music and/or want to write (simple) real sheet music, the free version of Finale (Notepad) is pretty simple and effective. It will play back the music as well, and there’s other $ versions. I need sheet music, so I installed a PDF printer, printed to PDF and then used a tool to save that as a PNG. http://www.codamusic.com/notepad/new.aspx