Recently Google released their Flight-Search service, we think that is the biggest beta version EVER.
Yes, google has the best results and a lot of engineering to make the best things but today we have a lot of services with more "experience" and much better results.
Has a very simple interface (good point) like all the other google's products; If you wanna go from Washington to San Francisco you just have to "say it to google" and the service will return the cheapest day.
At this moment small cities and outside the US is not available ...
Let's wait some time to see if this products turns on or follows the same way of "Google Wave".