You can get the cheapest flights if you are flexible on the flight dates.

I know you wanted to beat Orbitz, ;-) but the Orbitz Deal Detector is IMHO a really good start:
http://www.orbitz.com/dealdetector/

Unfortunately you are not that flexible with the flight dates on Orbitz and playing around with your options for hours is somewhat cumbersome. This is where ITA Software comes in:
http://beta.itasoftware.com/
These are the guys who made the software that runs on Orbitz.com. You can log into their website and use the software from there. It gives you much more options to play with, like the "Month-Long Search" which will show you exactly what dates are cheapest to fly. I usually go right back to Orbitz and use the Day I found through ITA Software.

Southwest.com is always good for deals. They sometimes offer round trip flights for as low as $99 if you book far in advance (another important aspect to get the best deal). Check out Ding:
http://www.southwest.com/ding/
Haven't used it myself, but it looks interesting.

Sometimes you can get a good deal on Travelocity or Expedia so don't count them out just yet. It always pays to shop around and compare.

Once you settled on a fare, go here:

http://www.seatguru.com

To find out what seat you should select (if you have that option).

I hope this information was usefull. 

Amazingly I got the best deal to Peru from Expedia. It was far better than what Orbitz had at the time.

I watched the fares very carefully up to 3 months before leaving. When I finally had decide on when to go and had my trip all set up with the travel agency, the prizes on Orbitz had gone up quite a bit. Amazingly Expedia offered the best deal at that time (about 6 weeks before leaving). Had I booked earlier, I could have gotten a somewhat better deal from Orbitz which was gone at this time.

Andre Check out my Photos

There seems to be a new kid on the block.

I found this site:

http://www.flysn.com/

They offer pretty amazing deals. I think I will give them a go for my next flight.

Andre

Do these sites save you money on flights within the United States or are they mostly geared toward international travel? 

Most of them are good for all international flights. I do know that http://www.flysn.com/ works for everything even though I am only flying from the US.

Sites like Expedia have their local branches with country specific top level domains in other countries.

Andre

i normally use Travelocity when ever i am looking for cheap flights, they are very goood so you can check them out.

There's a site that does comparisons of different travel sites.  For example, I was seeing how much a round trip ticket would be from Kansas City to London, this site gave me a list of what several different travel sites would cost.  It ranged from $344 to $757.  I've never really used it, just happened across it and decided to check it out.  http://www.cheapflights.com/