I use
Windows Live Mesh. Free, allows you to sync files between several computers, not size restrictions, all syncing is done using your internet connection.
Often I'll travel with my netbook rather than the laptop I use as my primary computer. If I leave my laptop running at home (display off), then my netbook automatically syncs files on the two. Always nice if you're worried about a computer getting lost/stolen. When I get home, all of my photos, work files, etc., are already up to date on my laptop.