Try to go to expedia or travelocity like these folks said. I wouldn't purchase the flight from them, I would use it as reference as to who has the best deals. Once you see who the cheapest is on those two sites, go to that airlines own website, sometimes you can get it cheaper doing it that way. For example ATL-PIT on Delta was 141.50 on travelocity after taxes and crap, go to delta.com it was 136.50. Save five dollars, gas money to get to the airport.
KK