Mac only: Online backup service Mozy has released the final, 1.0 version of their Mac client, which doesn't have all the options that the PC side does, but still gets the job done. Choose which folders you want to back up on Mozy's servers over an encrypted connection, or simply back up your entire home directory, or pre-suggested sets of files (like your Address Book, iCal, Application Preferences, etc). I've actually plunked down the $5 a month unlimited storage at Mozy costs, and I use it on both my Mac and PC. Overall the service helps me sleep better at night knowing I've got off-site backup and and doesn't slow down my computer or work too much. I've only got one complaint.
Since I've got a relatively small hard drive in my Macbook Pro (which is split with a Windows installation in Boot Camp), I keep my full iTunes library on an external FireWire drive. Mozy can and will back up files on a FireWire drive, but if you disconnect the drive (say, when you're traveling), on the next backup, Mozy will delete the drive's file backups on their server. Next time you mount it? Mozy re-uploads everything from it again, which is a long and tedious process, depending on the size of your drive. If Mozy could be smarter about that, I'd be completely satisfied. Mozy offers a free 2GB trial to start, and Mozy Home will set you back $5 a month. Clients for both Mac and PC are available.