I have used several programs in the past and the one I have personally settled on is called "Audio Hijack Pro" from Rogue Amoeba:http://www.rogueamoeba.com/audiohijackpro/
It is easy to use and I'm happy with the results. There is an accompanying piece of software called "Fission" that is great for splitting and naming tracks. I thought I'd mention these progs as you say you're a Mac user and these are Mac only programs.
Oh yeah, Audio Hijack lets you record from the Internet as well which is pretty cool for recording radio.
Seconded on Audacity though, it is a great program especially considering it's free!