Pledgehammer.com is a site that helps you keep your promises. It makes your pledge public and asks you to decide on a deadline as well as a financial incentive. Should you not succeed on your promise, it encourages you to donate money to a charity of your choice.
Some pledges include:
I pledge that every time I buy something new, I will donate something I already have or I will donate $7.00 each time I don't.
I pledge that I will send a balloon into space to take photographs by Sept. 30, 2011 or I will donate 250.00 GBP to charity.
I pledge to finish reading all the self-help books I've started, quit smoking and lose 30 pounds by Dec. 31, 2009, or I will donate 100.00 USD to charity.
You get the idea. It's fun, easy and an interesting way to hold yourself accountable.