After reading Dan's recommendation, I tried out SideStep for booking my flight to SXSW. He's right, it does have a convenient interface, but I was a bit leery because it had some monstrous installation that larded no fewer than six SideStep icons on my machine. Those are all safely deleted, and now I'm happy again.
Of course, I used their wizard to find the cheapest price, then I went to Priceline anyway. And Priceline gave me the same flight I had found on SideStep, but forty bucks cheaper. Cha-ching!