I'm a big fan of Digit, which has helped me painlessly squirrel away lots of money:
Digit, an automated savings account that opens to the public today for US accounts, hopes to put us back in the black. Let it monitor your income and spending habits, and it will begin socking away a few dollars whenever it thinks you won’t miss them. I’ve been using it for a month now, and painlessly managed to save $360 toward a trip I’m planning to take this summer. It’s the best thing to happen to my personal finances in some time, and it seems crazy that no retail bank has developed a system like this before.