music programs for mac?

Ableton Live for something akin to Sonic Foundry's Acid

Most anything by Native Instruments - esp. Absynth & Reaktor (softsynths)

Propellerheads Reason for a preconfigured dance production environment.

Max/MSP for the technically inclined. Most flexible software for music creation/manipulation, but worst learning curve.

Protools or Spark for pro-quality mastering.

Cubase or Logic for a powerful MIDI+Audio sequencing set-up.

None of these are free, but there is a free version of Protools that is quite handy..

I downloaded the free Protools for Mac and liked it so much that I went out and got a M-box too. Details at http://www.digidesign.com. If I had to do it again, I would've just stuck with the free ProTools and and a crappy microphone because now I can hear in clear detail just what a crappy musician I am.