Audacity is a free, easy-to-use audio editor and recorder for Windows, Mac OS X, GNU/Linux, and other operating systems. You can use Audacity to: Record live audio, Convert tapes and records into digital recordings or CDs, Edit Ogg Vorbis, MP3, and WAV sound files, Cut, copy, splice, and mix sounds together, Change the speed or pitch of a recording, and more! Read more Killer App
Cacophony is a powerful yet easy-to-use audio editing application available exclusively for the Mac OS X platform.
(commercial) Fission is a streamlined audio editor designed to get you editing in minutes, not hours. It works with both mono and stereo MP3, AAC, Apple Lossless and AIFF audio, enabling you to instantly trim and split files with no quality loss.
(commercial) JamDeck is an organic music sketchpad for capturing ideas quickly.
Loop Editor is a simple audio loop editor. Designed in Cocoa, Loop Editor takes advantage of Quartz, CoreAudio, and other solid OS X interface features.
Portable Audacity OS X is the Audacity audio editor packaged as portable application so you can carry around with you on any portable device, USB thumb drive, iPod, portable hard drive,memory card, other portable device (also on your internal hard disk) as long as it has 13.2 MB of free space and use on any Mac OS X computer, taking your preferences with you.
(shareware) TwistedWave is an audio editor that supports many formats. Among other things, it provides a very fast interface. It supports unlimited and instant undo and redo and imports from and exports to many formats.