I second the Rsync recommendation. I back up our servers every 15 minutes with it. In the event of a catastrophe, we will have lost 15 minutes worth of data, at most.
Yes, rsnapshot is excelent. The documentation is good too.
We also use gpg (gnupg.org) to encrypt our critical databases and code repository and send them to Amazon S3 every night. I started doing this after the last earthquake here in the bay area (which was centered near Freemont, where our colo is). I have tattooed the key to unencrypt them on my inner thigh.
