I currently back up my main laptop onto external hard drives but that is monthly and ...well I miss some months.
Tim suggested carbonite. (www.carbonite.com) and I set up an account with them and love it!
Our business system computors get backed up automatically within our network to a RAID NAS drive but my laptop is often "a cowboy", disconnected from the network and needed a different solution.
Carbonite so far looks great!