mAC3dec is an AC-3 audio decoder for the Macintosh, used to decode the AC-3 audio used on DVDs and convert to AIFF or MP3. mAC3dec can also read QuickTime files, AIFFs, WAVs, Audio CD tracks, and more.    

Sound Studio is an audio editing and recording application for Macintosh computers. It features two-channel editing, several effects filters, sample rate conversion, and support for many file formats including AIFF, SDII, WAVE, and QuickTime movie...

SoundMachine is a AU/AIFF sound recorder and player application.  It can also open other applications and find sound resources to play.  SoundMachine also allows you to play sounds at different sampling rates.