you can't beat dropbox.com. Dropbox is natively compatible with Linux, Mac, and Windows. Basically your 'dropbox' is a directory on your system. Anything you put into this directory (or on linux you can additionally create sym links from other directories within) will be automatically synced and backed up. Dropbox also has an add on service to roll back files and directories to previous revisions...it's kinda like a combination between file backup and revision control. Currently they only allow up to 100GB accounts, but I'm fairly certain they're working toward a higher limit in the near future
. The account pricing starts at FREE for 2GB, then goes to 9.99 per month for 50GB, and 19.99 per month for 100GB. I currently own a 50GB account. Their web interface is also AWESOME for anywhere access. because of the quick sync feature, you can also store stuff like password databases, browser profiles, etc in your dropbox and any computer connected to your dropbox has access to the same files. You can also selectively choose which folders sync on which computers with their newest software. If that isn't enough, there are apps for both iphone and android. Dropbox is hands-down the best option out there for backup/sync today.