Audio Hijack Pro is an affordable audio-recording workhorse for the Mac, capable of capturing audio from applications, devices such as microphones, or any other source that runs through your machine.
Audio Hijack Pro's clean, two-paned, iTunes-like interface focuses on sources that you can capture--which means just about anything, from software to hardware. By default, the left pane includes some of the usual suspects that you might want to record (DVD Player, iChat, iTunes, QuickTime Player, RealPlayer, Safari, Skype, your system audio, and default system input), but you can easily add additional sources, such as other apps or devices.
You can define all sorts of settings for any source in the app's right pane--including recording schedules, tags, and a wide range of audio effects--and this is where you'll find most of the muscle in Audio Hijack Pro's feature set, such as the ability to quickly define formats and run scripts (whether with Automator or AppleScript). At the same time, even more casual users will find a lot to like in Audio Hijack Pro, such as one-touch recording for Skype and iChat conversations.
Audio Hijack Pro won't help you edit audio--you'll need a good editor for that--but it's an excellent, all-around value for anyone who wants to capture audio on a Mac.