Perhaps you really like flying on one particular airline...but they don't fly to your destination. So you need to check several different airlines in order to find the best deal or the best times to fly.
If you are like me, you have your favorite places to check flights, fares, deals and more. Some of those sites even compare several airlines or different booking sites for one destination, all at the same time. Those are a great place to start your search.
Google recently acquired ITA Software, one of those comparing sites. As a travel data clearinghouse it supplies everyone from Bing to Orbitz to Kayak with their flight information, according to Budget Travel.
Founded in 1996 by MIT computer scientists, ITA Software isn't new but now it's easier to look at and use. Keep in mind you cannot book from this site but it is great for giving you all the tools in one spot.
It might be worthwhile to check it out at http://www.itasoftware.com/.