Google Flights is clean, easy and ridiculously fast. And it all happens on one screen.
if only there were a website somewhere on the internets where one could compare flight costs and routes...
Its engine helps users to get where they're going, without any crazy distractions like ads or, you know, color. It's straight-up Google interface: no nonsense and ridiculously fast/accurate -- but only for domestic flights. International search-and-return is in the pipeline.
Just set your home airport and click on the map for instant-return results. Entering search parameters, like time of departure or airline or price, is pre-set on sliders or directional arrows: slide in one-hour increments; click for $50 ups and downs.
Possible flight paths expand to show possible return flights and their prices. They also collapse up with rapidity, when clicked.
The display map shows the flight path (so you can spy all the fly-over states you're missing). It also pre-populates sample fares to cities before you choose your real destination. (This could be distracting in that you might be reminded, "Oh, I haven't seen (that friend) in Chicago in a while..." and then, bang, you're out $341 and a weekend that you hadn't planned.)
Users can set limits, like price or duration, as well. You can hide the map, too (but why?).