We use the system back up built into Windows to back up my wife's computer. It seems to work pretty well. If you have a spare computer with internet access Windows Live Sync can work well if you save all your important stuff to a specified folder. It's been a while since I've used Live Sync but it used to be free. I have ours set up wirelessly. The biggest draw back to this (and the live sync) is that it's slower than having something hardwired, but it has that convenience factor.

Depending on what kind of solution you're looking for I would suggest a couple different things 1) Google Docs- allows by default 1GB of storage, but extra storage can be bought for $0.25/year per GB. You can upload any file type to it and if it's compatible with google docs format (ie. documents, spreadsheets, presentations) it can be edited right on the site. I use this for cloud storage of papers, collaboration for notes (folders or specific documents can be shared)

2) Windows skydrive. This gives 25 GB of storage and you may even already have a windows live ID (if not it's free to sign up) This is good for free bulk storage, but the only problem comes when you want to edit a document quick, because you need to download the copy, change it, then re-upload it. That's the advantage google docs has over skydrive.