For a full system image backup tool, clonezilla is really nice.
You can boot off a CD or a usb stick and clone partitions or disks over the network to some network drives. The iso CD image is about a 90MB download. You can backup to ftp, smb, ssh, or local usb attached drives.
It doesn't backup the whole size of the image, only the space you have used on your disk. So if you have a 600GB drive, and only use 40GB it'll only backup the 40GB. It can even compress the saved images with various forms of compression(gzip, bz2, lzo etc).
The only downside is that you need to take your machine offline to do so.
However to save a lot of time restoring your OS(s) in the future, it's a really good tool.
It's based on linux, and is free to use/modify. It works on apple hardware, but only has experimental support for backing up OSX partitions... but I think it works with full disk images. It works fine for windows, and linux partitions of course.