Change the software in your media player with RockBox

Rockbox is an Open Source replacement firmware for portable digital audio players

Supported Players:

• Apple: 1st through 5.5th generation iPod, iPod Mini and 1st generation iPod Nano
  (not the Shuffle, 2nd/3rd/4th gen Nano, Classic or Touch)
• Archos: Jukebox 5000, 6000, Studio, Recorder, FM Recorder, Recorder V2 and Ondio
• Cowon: iAudio X5, X5V, X5L, M5, M5L, M3 and M3L
• iriver: iHP100 series, H100 series, H300 series and H10 series
• Olympus: M:Robe 100
• SanDisk: Sansa c200 series, e200 series and e200R series (not the AMS models)
• Toshiba: Gigabeat X and F series (not the S series)

Link:
http://www.rockbox.org/