I use Time Machine.
For Linux I just use rsync. Restoring a failed Linux system often requires fiddling with Knoppix as well; get a nice recent Knoppix disc burned and ready to go in an emergency.
Don't forget: have more than one backup, and have an offsite backup.
I never really tested my Windows system backup solutions; I decided to abandon Windows instead. For backing up Windows files I used to use SyncBack: http://www.2brightsparks.com/downloads.html -- it was pretty good.
I need to work on doing better online backups. A lot of my work is web stuff, though, and that lives on other servers anyway.