www.rockbox.org

          Rockbox is an open source firmware for mp3 players, written from scratch. It runs on a wide range of players: 

         Rockbox runs well on these players, has a complete manual and is supported by the installer:

• Apple: iPod 1g through 5.5g, iPod Mini, iPod Nano 1g and iPod Nano 2g
• 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
• Packard Bell: Vibe 500
• SanDisk: Sansa c200 (not v2), e200 and e200R series, Fuze, Clip and Clip+
• Toshiba: Gigabeat X and F series

         Rockbox runs on these players, but is incomplete, less usable or has problems that limit it to advanced users:

• Cowon: D2
• MPIO: HD200, HD300
• Olympus: M:Robe 500
• Philips: GoGear SA9200, GoGear HDD16x0 and HDD63x0
• Samsung: YH-820, YH-920 and YH-925
• SanDisk: Sansa c200v2 series
• Toshiba: Gigabeat S

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