The gold standard for OS X volume duplication seems to be Carbon Copy Cloner by Mike Bombich. This application is really nothing more than a nice GUI front end for some command-line tools already installed with OSX. CCC makes it easy to create an identical, bootable image onto a second drive or FireWire/USB drive connected to your computer.
If you're looking for a way to back up your hard drive over a network, check out NetRestore, also from Bombich Software. Both CCC and NetRestore are free.
If you're handy with the UNIX command line, you can also back up your hard drive with rsync. Step-by-step instructions can be found here, written by Matthew Phillips: Backup Your Mac With rsync (Thanks to jDyno for sharing the link).
There are commercial products available as well, the popular Dantz Retrospect product line has Mac products for both personal and business users.