[Osmium]

This looks cool, but of course you can also use encfs directly with Dropbox or, if you prefer a graphical interface, Boxcryptor[1] have a fork of encfs specifically for cloud storage along with some platform-specific apps.

[1] https://www.boxcryptor.com

[Tho85]

I used that combination before, it works really nice. But at some point I hit the storage limit and had to come up with a self-hosted solution.