Zling has a minature backup device for digital cameras. The Photo-Wallet uses 1-inch hard drive, and is available in three capacities: 1GB (US$69), 2GB ($109) and 5GB ($149). It has two slots, one for s SD/MMC and one for CompactFlash memory cards.
It has a rechargable battery built-in, and comes with a charger. No indication of how long the battery lasts. It measures about 3.5" x 2.5". A USB2 connector is for computers, and the unit is recognized as an external drive by Windows ME/2000/XP computers without needing drivers -- that's good for copying files to friends' computers.
This might be a good way to back up your photos when travelling. I'd go for the 5GB model, which would hold about 5,000 photographics or about 2 hours of AVI movies (15fps) created by the Canon S1iS.