Try BookingBuddy.com Noiki. You can compare prices among the sites. But for me, since I got to TX most of the time, I use Hotwire. To me they are the cheapest but the only suckie thing about them is that you don't know your itinerary until your purchase is finalize. So it's a high chance that you get the redeye flights.
Also, try Priceline too. I use that one sometimes when I have last minute flights to arrange. You can bid for a low price with them. Sometimes it work and sometimes not.