http://blog.auinteractive.com/how-to-get-the-cheapest-flight-every-sin...

Simple article with links to several airfare search tools that I hadn't seen yet...

My recommendation to get lowest airfare:

• Start with Farechase, Sidestep, Kayak, Farecast.
• Search Southwest and Jet Blue.
• Check the old-schoolers: Orbitz, Travelocity, Expedia.
• For good measure (and to be sure) check Cheaptickets, Hotwire, Priceline, Mobissimo, and Trabber.