Hipmunk - Cheap flights, cheap hotels, and travel Search

Because you're going to be traveling, might as well use the best travel search on the planet. Disclosure: I helped launch it.

I just tried it out now to get tickets for Irelands summit, it looks great. I must say that the interface is better than most travel search sites. The comparison option is also put in a good way. But I do not think it is the cheapest though. Nice logo!