Hipmunk

Hipmunk takes the agony out of flight search. With Hipmunk you'll see all the relevant flights on a timeline, helping you visualize the right choice. Unlike every other app out there, Hipmunk doesn't just show you the cheapest flight first — it instead sorts by "agony," which incorporates important factors like how long you'll be traveling and how many stops you'll make.

Hipmunk also makes booking easy. When you've found the right flight, you can either book it on your phone, email it to someone else, or finish on your desktop computer.