A few cheap ticket kinda sites:
cheaptickets.com
pinpoint travel
lowestfare.com
lastminutetravel.com
I would also try the following:
1) look at alternative airports. If you are renting a car there or if someone is picking you up, look within the acceptible driving range. For example, flying into Houston from NYC was 1400 round trip this week. 2hrs away, Austin Tx, 700 round trip and the car rental was $200 cheaper for the week.
2) check some of the major carriers (
www.aa.com) and see if they have cheaper flights on days +/- 1 or 2 days of your needed arrival/departure. Most of the main airlines will show you prices in a grid with this info. If you can go a day earlier or at ugly travel times, you can possibly save a bit of cash.
3) Avoid "hub to hub" flight routes. These would seem to be the cheapest routes since the airline flys them all the time, however these are most often the most expensive routes they have because they are direct flights. See item #1 above and then check airlines that will give you a connection flight. Another possible option, book a flight to omaha that connects in st louis and just dont get on the connection. The problem doing that is they probably wont let you on the return flight in st louis
4) Look online wed morning, like 1am ET for any deals. I would try to book 14days out, however thats usually when the 'cheap' rates get loaded into the systems and there's almost always deals to be had.
Another thing... unless the orbitz, lowestfare, etc have a drastically reduced rate, try to book with the airlines directly. The reason is *IF* you have any issues, booking via a 3rd party means you have to deal with the 3rd party. If you book directly with the airline, they will service your issues at the airport (should you have any) and get you on your way before the people that booked via 3rd party groups.
FWIW, I am on planes at least 4x a week, generally 8+ flights a week so let me know if you need more info