I used my Dell Axim X50v equipped with a 2GB CompactFlash card for this purpose while away for five weeks. My camera uses SD cards, and since the Axim has both slots, I was able to load both cards and simply cut/paste between them.

The Axim will take microdrives (similar to what is inside the iPod) in the CompactFlash slot as well if you want boatloads of capacity.

Just another option to consider. I almost went the iPod route, but figured the Axim would have more utility both during and after the trip (it can function as an MP3 player and GPS receiver, it has wireless Internet and Bluetooth, runs all kinds of programs, etc.) and was about the same price as an iPod.