The folks at MacZealots have posted an article that compares several Mac backup solutions, including SuperDuper! (my personal favorite), Synk Backup, Apple's Backup, iBackup and Crashplan, as well as some speculation on Time Machine.
In the end, SuperDuper! and Crashplan came out on top as the bookends of a comprehensive plan: SuperDuper! for a full backup to an external drive, and Crashplan for off-site storage of mission-critical files. This is pretty much what I do, though I hadn't heard of Crashplan until I wrote this post!
The important thing here - and we know you've all heard this a million times - is this: Back up your stuff!