Here is a great post about transaction types that may be possible now or in the future.
http://codinginmysleep.com/exotic-transaction-types-with-bitcoin/I really like the Assurance Contracts because how it can be done without third parties.
While they never use the term itself on their site, the most commonly understood example of assurance contracts may well be the popular crowd-funding site KickStarter. For those not familiar, a KickStarter contract happens like this: The project founder submits their idea and the estimated amount of money it will take to make that idea a reality. If the combined value of all pledges is greater than or equal to the amount they specified, they get the money and start work on their project. If the value of all pledges isn't enough, they get nothing and the money goes back to all the investors. This is another transaction type that would be fairly easy to implement in Bitcoin, with the added bonus of not requiring any third parties.