After gushing over Kayak's great flight search I realized I had not used Sidestep in some time and should give it a try.   In my opinion Sidestep used to really suck, requiring download of software to your browser and in my limited experience did not deliver good rates. 

Now, like Orbitz and Kayak, Sidestep allows easy browser based searching.  However for the 2-3 legged cross country flight I'm currently researching (MFR to BWI), Kayak blows away Sidestep and Orbitz with an American Airlines flight that is a whopping $200 less.  

This could be a quirk due to my rural Oregon location but I'm impressed nonetheless.  I also REALLY like Kayak's intuitive interface and the ease of selecting your previous searches very quickly.    Rates from the big systems are updated three times per day and availability can change even more frequently, so it's a good idea to search using the same criteria several times before you "give up" on a good rate.  Persistence pays in the bookings game and Kayak makes it easier to stay on task. 

Eventually I'll try to do a better more  balanced comparison where I'll pick a bunch of routes and run them on the different consolidation systems to see who wins, but first I'll do a few more of these quickie comparisons such as Kayak vs Yahoo's fairly new offering "FareChase".