Google is serving flight booking boxes in the Onebox (this is the area beneath the PPC ads but above the organic results).

Check out:

http://www.google.com/search?hl=en&q=dublin+london

(UK users, your browser may default to our local datacentre. When it does go to the Google.co.uk homepage and click on the Go to Google.com link in the lower right or try clicking here first. )

It comes up when a departure and destination airport code IE: LGA (LaGuardia Airport New York), or full departure and destination airport are entered. This is probably a US only trial with current advertisers being the usual suspects Expedia, Hotwire & Orbitz.