My iPod nano 5th gen suddenly quit showing up in Finder and on iTunes. The iPod would not stay connected. It seemed to connect, say it was connected, but still not show up in Finder or iTunes, then reboot after a few seconds of being connected. I tried changing cords, tried connecting to other macs, even tried connecting to an old Windows machine. It would simply not connect or show up on any system dashboard.
I finally came across this link which helped me fix the problem: http://support.apple.com/kb/HT1363
I followed the steps to put the iPod into "disk mode". This worked. I was able to successfully connect the iPod while in disk mode - it was recognized in iTunes. iTunes immediately reported that the iPod was potentially corrupted and needed to be restored. I happily clicked "restore", then resync'd my music and now everything is back to normal.
I hope this helps any one else who might have the same problem.