How can I record sound in Mac OS?

Is there any simple application (or built-in in Mac OS) that allows me to record sound on a Mac? I'm referring not only to voice input through the mic, but also to sounds issued by the system.

Audio Hijack and WireTap Studio are both application suites for recording audio from any input, include the system audio. They're not fee, but their trials might suffice.

A simpler solution would be SoundFlower which acts like an output to which system audio can be sent, then used as an input source in any audio recording program, even quicktime. If you want to be able to hear sound from your speakers/headphones, you'll need to run the sound flower bed app, which takes sound flower's audio coming in from your system, and forwards it to your speakers/headphones while still being able to use it.

You want Audio Hijack Pro. Records system audio, from long time quality Mac developer, Rogue Amoeba.