I find Bitcoin already quite an impressive achievement. It is the first digital currency without central point of failure (in the physical world, gold can be used for that).

Also, consider rouleth.com, which is a provably "fair" online casino. (The odds are still against you, but you can verify that the bank did not cheat when you lose ten times in a row.)

Or imagine companies with shares on the blockchain, combined with smart contracts. That would allow you to automatically enforce all kinds of shareholder agreements (for example vesting or a tag-along right).

Maybe that's not revolutionary, but it could be quite useful and save a lot in legal anf auditing fees.