Search on Bing for the phrase "fly to..." and the name of a major destination city and you will now see an automatic display of the best dates to fly from where you are to that place, with the lowest price for a round trip ticket and advice about whether the price is likely to go up or down if you waited to buy the ticket later. It's really cool.
I don't know if I'm going to change my travel dates or destination based on a difference of a few dollars, but this is at least fun. It's really fast and easy to see cheap flights and dates at various places. Click through the results and you'll see even more, much of it powered by Microsoft's very wise acquisition of airfare prediction company Farecast in 2008.
Google has a big travel search acquisition of its own in the works of course. It's looking to buy ITA Software, but that deal is super controversial and faces regulatory challenges due to concerns about monopoly power.
Presuming Google can buy ITA, it will be interesting to see what it can come up with to wow users performing travel searches. That is ultimately, after all, what it's all about in the end.