I just learned of a free, online backup service that creates a folder on your computer where you can drop files. Anything you put in the folder is then securely uploaded to their website (great for backing up important files). Better yet, you can install it on multiple computers—both Macs AND PCs—so you can send large files back and forth from one computer to another, or from one family member to another.
It's called DropBox. DropBox gives you 2GBs of storage free, so you can backup a fair amount of stuff (if you want to store more than that, you can always buy more). It's just a super easy way to synchronize and/or back up important files. You can even drop photos into it, and get a web link you can send to send friends and family so they can view the pics. Also, consider Box.net which has an iPhone app.
For those of you who are too lazy to drop files into a desktop folder, and just want to back up your whole machine online, I've come across the scrappy kids at BackBlaze. Just install their application, configure it, and it'll back up any file changes you've made every day (without slowing down your machine) for just $5/mo. They are more affordable because their servers use inexpensive off-the-shelf hardware and software. (BTW, if you sign up with them, I get small-kickback, too…)
Just remember, it's not a matter of IF your hard drive will crash harder than the stock market, it's a matter of WHEN.