REAPER (short for Rapid Environment for Audio Prototyping and Efficient Recording) is a powerful and professional multi-track audio recording, arranging, editing, mixing and rendering tool primarily designed by former developers from Winamp. It is suitable for both audio enthusiasts and professionals.
Cool Edit Pro (its next generation of successor is the current Adobe Audition) is a powerful, excellent multi-track recording and digital audio editing software developed by Adobe Systems company. Many users described it as an "audio painting" program, which is enough to see its technical background with flexibility and usability.
Audacity is an open-source and cross-platform (Windows, Mac OS X, Linux) live audio recording and editing freeware. It is developed under Linux, has a point-and-shoot operation interface and professional audio processing functions and effects.