Do you think you can find a hole in the Google Chrome browser? Google's willing to pay you between $500 and $1337 (clever) for each and every one found. This challenge is Google's way of showing confidence in their browser, and at the same time getting security experts to once-over the open source browser.
Any security related bug classified as high or critical priority in the open source Chromium or Google Chrome branch (stable, beta and dev) qualify for the prize.
That said, $500 - $1337 isn't a lot of money though -- some zero-day exploits can be sold on the black market for hundreds of thousands of dollars. It will be interesting to see if security experts take the bait on this one.