I use Orbitz for booking a lot of work travel or at least looking up options and I think nearly all of them show up there (including Spirit and Frontier). As you mentioned, Southwest does not show up on the major search sites. Neither does Porter, which is a small airline with service to a small airport in Toronto.
I prefer Orbitz because I like how it is set-up and find it more user friendly for what I need.
Jet Blue shows up on Kayak now. They don't quote Southwest but usually if it's available on the route it will show up on the list of airlines on the left and you can click through to the site.
Great! Also, just so you are aware, Orbitz offers price assurance where if someone else books your same itinerary for less at any point after you, they will send you the difference. While it doesn't happen often, I have had it happen at least 4 times over the years. Each time was a nice surprise.
I just booked tickets to the Caribbean. It was incredibly frustrating. Using Travelocity and Orbitz allowed me to see many flight options, but they kept showing me connections as the only available option and that direct flights were hundreds of dollars more. I checked united.com, just out of curiosity, and found a direct for $20 more and at better times for us.
Not that this helps, but I just found it frustrating and that there might not be just one website that will be the best. I find that when searching for flights, you need to check several sources.
Sometimes I look on the website for the airport where I want to go and look at arrival and departures to see what airlines serve that airport. Sometimes you find connections you didn't consider - I was booking travel to Montrose, CO and saw AA had a flight from Dallas - opened up possibilities as I was only looking thru Denver.
So - where do I book the flights I find on itasoftware? When I go to the airline's site, it gives me a higher price. Is there an online booking agent? Or do I have to call an old fashioned travel agent?
jeffl