Ah, yes, an area where I (like to think) I'm an expert.
My advice - Orbitz usually finds the cheapest fares, but tacks on a significant fee. So here's what you do:
1) Search Orbitz. If you're flexible on what days you go, go into the full search page, and "search with bonus days."
2) Also, try a bunch of different departing and returning dates, if you're very flexible. Tuesdays, Wednesdays, and Saturdays usually have the cheapest fares.
3) Once you find a fare you like, note the flight numbers and departure times.
4) Go to the airline site, and search "by time" (NOT by price) for the exact flights you found on Orbitz.
5) You can then find the same fare Orbitz found, but without the Orbitz fee!
Note that when I've searched AA.com (American's site) by price, I usually do NOT find the cheapest prices, but this method will find them on the AA site.
Another idea for finding cheap tickets. Go to Travelocity.com, put in your departing and destination cities, and click "my dates are flexible." It will come up with a bunch of fares on different airlines. Click on one of the cheap ones, and it'll give you the days it's available. Try this for many airlines, you may get a really good fare.