There's also Renoise (http://www.renoise.com/) which is inspired by old school mod trackers. There's a free demo, and the full version is really cheap.
Consider looking at the See also section for a list of DAWs: http://en.wikipedia.org/wiki/Digital_Audio_Workstation#See_a...
http://audacity.sourceforge.net/
Free/open source, for Windows, OS X, and Linux.
Overall I'm not a fan, but I come from a background in more complex/full-featured DAW's like Logic and ProTools. I also find the UI lacking. That said, it's a great way to get off the ground when starting out with digital audio.
Sony ACID (I use ACID Pro extensively, free trial, free lite version)
Ableton Live
FL Studio
energyXT (Linux and Mac versions available)
Other stuff to check out: console.jp, Audiomulch