mplayer can take pretty much any video and output a pcm wav. ffmpeg can do certain types to wav, mp3, ac3, ogg vorbis and more.
VirtualDub can do AVI's and mpg's. VirtualDubMod can do AVI's, mpeg1 and 2, mkv and ogm's.
Graphedit can convert anything that windows media player can play.
BeSweet I am pretty sure can accept AVI's as input.
Some wav editors can open audio from AVI's and mpg's.