If you work on multiple computers, and want to carry files around with you OR need a quick backup storage...
My favorite toy is the portable USB thumb drives. They are getting cheaper and hold more information all of the time.
If you are looking to backup your photos and music, I would go to something larger and less portable. They now have reasonable, external, USB hard drives which are a better solution for that.
Many of your MP3 solutions can serve in this capacity as well.
One of the things I like about my Sony camera is that it is reconized by the computer as a portable drive, so you can copy files both to it and from it without needing any special software.
