If you like to rsync/rdiff your backups to an EBS volume on Amazon, this script will spin up a spot instance, attach the volume, run your backup, detach, and cleanup. A little bash knowledge and EC2 knowledge is required.
Original from http://roeeb.blogspot.com/2010/03/backup-to-amazon-ec2-using-spot.html (who seems to have got it from http://blog.blackpepper.co.uk/black-pepper-blog/Using-Amazon-EC2-EBS-S3-for-automated-backups.html ) but I cleaned it up a bit... a lot. And I've added micro-instance support as of Sep 10 2010.
Update: Here's a script that'll snapshot a given volume, keeping N snapshots, deleting older ones. http://www.thesatya.com/code/ec2-snapshot.bash-dist