Dan: I use a Western Digital Passport portable drive for backing up photos and others important documents. I works off of USB power only, no other power supply is needed. It's small and easy to transport. I think you can get them up to 250GB these days. Highly recommended. A great solution for backing up photos. You may want to look at their My Book Series which is not a portable but still works off just the USB drive and has excellent capacity to price. Bob Taylor