Mint is a personal finance service that may be the coolest thing I've seen so far at TechCrunch40. Plug in your account info for banks, credit cards, and other financial relationships you have, and it'll aggregate all your deposits and debts in one place. It'll remind you about bills that are due--via SMS if you like--and analyze ways that you might save money.
Part of this is in the form of advertising--Mint is free, but it'll present you offers based on its knowledge of your finances, such as a VoIP deal that's less than what you're currently playing for phone service. That sounds annoying and intrusive, but you only see the offers if you click over to a tab that lists them. The Mint demo also made a big deal about your Mint membership being anonymous; I guess that's true in the sense that it doesn't ask for your name, but giving a service access to all my financial information and accounts sure doesn't feel anonymous.
Overall, though, Mint looks slick and useful. Upon first blush I thought it was a competitor to Yodlee, a service I've used for several years to tally up my financial life. Turns out that Mint actually builds on Yodlee--with which it has a relationship--with a lot of new features and a more modern user interface.
Mint is supposedly going to go live momentarily; of everything I've seen so far, it's the one thing that makes me think "I'm going to sign up for that as soon as I can..."
I have tried the alpha and beta version of Mint, and it is fantastic! All of my finances are all in one place, and I can access all this information from any computer. And it's free! My favorite feature is that they will send you an email (and soon a text message) when you have unusual account activity or when you have low account balances. I thought that the ads on the Mint page would concern me inititally, but the ads are so personalized and you actually have control over finding them on the site - they do not pop up and are not on the side of the page.
Overall, Mint is ten-fold better than any of the personal finance software out there, and I think Mint is going to be a huge hit.