Permacoin
From Just Solve the File Format Problem
Permacoin is a proposed system developed at Microsoft Research that is both an electronic currency and a distributed filesystem. (And a floor wax and a dessert topping! Well, not quite.) It proposes to build a Bitcoin-style distributed crypto-currency system where one effect of the "mining" operation is to store data, which can be used as a file backup and retrieval service.
A similar concept is being implemented by Storj.
