Cloud Backup Options for HD Attached to Time Capsule
For cloud/online based backups here are a few to consider:


Backblaze 
Mozy 
Carbonite
Crashplan


They are all mostly the same - you install their software, pay an annual or monthly fee and your data is constantly backed up to their servers. A few offer more advanced features like mirroring to their servers and another machine.

I've put Backblaze at the top because thats what I use at home to backup my photos and music. Its cheap @ $50 per year for unlimited storage. I set it up once and never had to look at it again. Last week I recovered a folder of files through their web-interface, though you can (like most cloud backup companies) order a hard-drive with the contents. 



Another more DIY solution is using AmazonS3 combined with a backup program like GoodSync. You use S3 for the storage and then setup your backup/sync options in Goodsync. We use this at work to backup important project files. The advantage of this method is you have the same level of control you get when using backup software (timed backups/backups when files are changed/email notifications/advanced file comarison etc)

Here is a good starter article for AmazonS3 backups. Its also worth noting that AmazonS3 might end up being more expansive than a regular cloud backup service. You can calculate how much S3 would cost using their Simple Monthly Calculator