Rogue Amoeba's must-have audio tool Audio Hijack
lets you record audio from any Mac app; today's 2.2 release adds lots
of new features for automatically handling recorded audio. You can now
automatically add recorded audio to your iPod, or set a 'stop recording
after' option for easy scheduling. The release also features better
RealPlayer media handling, among other tweaks.

Compatibility: Mac
Pricing/Availability: $16 new (free upgrade), available now

UPDATED: Check out this in-depth tutorial on Audio Hijack to get started with the program!