Saving wallets

• If worried about getting hacked, you can write a contract such that person A can withdraw a maximum of x% of funds in a day and person B can withdraw a maximum of x% of funds in a day but together, they can withdraw anything.

Crop insurance

• Farmers can hedge their crops by purchasing derivatives contracts that pay out inversely based on weather conditions.

Decentralized Data Feed

• This could work where N parties all put into the system the value of a given datum, say ETH/USD price. The values are sorted and everyone between the 25th and 75th percentile receive one token as a reward. This way, people are incentivized to provide the same answer as everyone else which will most likely be the correct answer.

Smart Multisignature Escrow

• Allowing x different keys to interact with a given fund (i.e. 3 out of 5 keys can spend up to 10% per day while 2 out of 5 can spend up to 1% per day).

Cloud Computing

• Ethereum technology can create a verifiable computing environment where users ask each other to carry out computations and then optionally ask for proofs that computations at certain, random checkpoints to see that things were done correctly.

Peer-To-Peer-Gambling

• Many gambling protocols like Frank Stajano and Richard Clayton's cyberdice can be implemented on the Ethereum blockchain.