I would also recommend Reaper, although you really *should* cough up the $30 if you're going to really use it. I've heard of Kristal being used with good success.
Just a bump because they're FINALLY working on an OS X port of Reaper:
UPDATED May 8 2008 -! v2.206pre1/OSX0.895 mac preview build... - Cockos Confederated Forums