+1 for the Asus eeePC 900, 8.9"x6.5"x1" and 2lbs for $550. I use the Linux version and it works nicely.
I use it more as a communication device than for storage. I upload photos from my camera and then post
or email them to something like Flickr, then I delete them from the PC, still 16Gig is plenty of stortage for me. It takes SD cards so that's a way to store lots of photos. It's easy to surf and write journal entries on it and it easily fits into a handlebar bag.

The iPhone is an alternative. The new one looks great for touring and will let you do everything you want. The only issue is the keyboard, it's a pain to write large amounts of text with it, but it can be done. the advantage is the GPS etc and the light weight. It incorporates everyting you need, GPS, ipod, phone, web, email, camera.