For the Linux enthusiast, here a guide to some powerful, open-source audio editing apps for Linux. There are some outstanding audio tools for Linux such as Ardour, Audacity, and SND. The author talks a bit about why Linux is a excellent platform for this kind of work. http://arstechnica.com/guides/tweaks/linux-audio.ars
Linux does seem to be making some inroads in pro audio. There seems to be a lot happening in the Linux audio world including the Linux Sampler project which Benno has posted about.