Crashplan has a home plan that lets you back up unlimited data for all your machines. It works on Windows, OS X, Linux and Solaris, which is great for me; I back up all my machines to both the cloud and my Nexenta/Solaris NAS, as well as backing up the NAS. In fact, if you know other people who have lots of storage, you don't have to pay for Crashplan at all; you can back up to them, with encrypted data.
Backblaze really shines if you have a single Windows or OS X PC with a lot of data. For $50/year, it will allow you to backup unlimited data for a single computer. As far as I know there is no student discount.
SpiderOak really shines if you have multiple Windows, OS X or Linux PCs with a small amount of data between them. For $100/year, it will allow you to store up to 100GB of data between as many computers as you want to back up. If you're a student, it will only cost $50/year.