Aggregators

Mere months ago, the aggregator sites (such as Kayak and SideStep) were mostly good for airline flights, and few travelers used them for much more than that. Times are changing. The aggregators -- especially Kayak, as I will explain -- are probably the best place to figure out the range and location of the best car rental deals; the snapshot you can get of car rental rates is quite impressive.

A search on Kayak.com displays prices not only by rental company and airport, but by car class as well. And where you can toggle airlines and nearby airports and on and off when doing flight searches, you can do the same for car classes and rental companies for car rental searches. Kayak also lets you filter results by price range and options like automatic transmission and unlimited miles, and permits you to open up your search to include off-airport rental companies, where savings can be significant.

Among the aggregators, Kayak is leading the way with car rentals. SideStep, which is outstanding for flight searches, restricts each individual search by car class, offering a far less comprehensive look at your price and car class options. Meanwhile, Yahoo!'s Farechase, which emerged as Best in Class in some comparison testing I did last year on airline pricing, searches only flights and hotels at present.