Ken,
Also take a look at Kayak, but keep in mind almost ALWAYS the air carrier, just like hotel sites, give the best rate and you have someone to call. Having said that you can bump into great trips on third party sites. If you are willing to play games, and Kayak is good for that, try for example flying into point A and then flying out of point B.
Sometimes that type itinerary can offer some great savings. I do not know the trip you have planned, but be flexible and you can save a bunch. We are leaving for Europe in a couple days and I used frequent flyer miles so that does not count, but our friends got roundtrip from DC to Switzerland on the way and return from Amsterdam to DC for around $600. That is a good price. Just play the game - you can win.
