Audacity
Simple sound recording tool.

Media Coder
Great tool for ripping CDs, DVDs, etc and converting between tons of video formats.

Handbrake
DVD to MPEG-4 ripper/converter. (Use this to rip your DVDs for viewing on your video iPod)

MP3 Gain
Easy to use MP3 manipulation tool for Windows, adjusts sound levels on MP3's so they are all the same.

MP3 Book Helper
This program provides rapid Mp3 (ID3v1, ID3v2) and Ogg/Speex/Flac Vorbis tags editing and file renaming functions. Mass Tag editing is done using special variables and Regular Expressions.

Media Players

musikCube
Open Source MP3 Player, ripper and organizer written using the .NET Framework

Media Player Classic
Compact, but powerful media player.

VLC
Plays more video files than most players: Quicktime, AVI, DIVX, OGG, and more. Pretty good interface with ability to do cool tricks and streaming.

MPlayer
Similar to VLC-- plays loads of video formats. (Somewhat complicated install process)

Democracy Player
Beautiful interface. Plays any video file. Subscribe to video RSS feeds, download and watch all in one app. Torrent support. Search and download from YouTube and other sites.