Dropbox is a simple file synchronisation service for multiple computers. It's your granny's rsync, if you like. Installation is simple, as is signup. You point the software at a magic folder that it will keep in sync with every other computer tied to your Dropbox account. It's simple, fast, and works well.
The free version offers 2G of space. You can pay for more, if you need it. If you're not on a machine with Dropbox installed there's a web interface for you to access your files.
It's working really well for me. I'm working on my presentation for this year's ACCU conference, and Dropbox is making my life easier. Rather than carry around the presentation with me to edit at work or at home, I just save it in my Dropbox folder, and the latest version is ready for me to edit wherever I am.
Check it out.