CDex : Encodes and extracts audio. Handles WAV, MP3, OGG, VQF, APE and more.
mp3DirectCut : Allows direct editing of mp3 files withOUT recompressing the file.
Foobar2000 : A music manager/player. Optional decoders are available. Recommended by havdi, a GeoShell user.
QCD Player : Recommended by Pistos, a GeoShell user, who said, "Best skinnable audio player I know... (as compared to Windows Media Player, Real Player, WinAmp). No ads or spyware."
Media Monkey : A new program for tagging your MP3s AND adding album artwork to the files.