http://www.jungledisk.com/
Another alternative.
Microsoft is getting ready to launch their cloud computing solution (like Amazon S3) and rumour has it that they're going to undercut the costs significantly, so that might be an option too (not using the cloud computing portion, just the storage).
I've been thinking of doing this, slow transfer isn't that big a deal, you only have to upload something once.
But I probably wouldn't back up all my media (kids' ripped DVDs, etc), just the more important stuff, then a few GB would be plenty. Then use local backups for the bigger stuff (I have mirrored drives on a NAS).