Ripcorder Audio is an app that can be used to record from any audio input device, including Mac’s internal microphone and built-in line input. You can even set it up to record your system's sound. Thus, you can easily record your favorite online audio stream, such as a radio broadcast and a podcast. You can then import and play back those recordings using iTunes or any other audio player.
You can use Ripcorder Audio to record directly into common formats, such as MP3, AAC, Apple Lossless, PCM, FLAC, etc.