I highly recommend Farechase, which we acquired a while back. It’s basically an airfare search engine, but it’s awesome because it searches everything, including low-cost carriers like JetBlue and Southwest, and presents everything by price and number of stopovers. There have been things like this before, but I’ve never seen anything as fast and clean. The only downside is it only works for IE at the moment, but yeah, it’s pretty much the only airfare tool I use nowadays. It’s awesome.