- Flystein is a personalized CHEAP flights hacking service. Their experts use insider industry knowledge & technology to find the cheapest flights online. They use hidden city ticket and far more advanced techniques to save the most money. www.flystein.com. Check out this article that outlines how much they can save and how it works - http://dereklow.co/the-best-webs...
- I've found that Skyscanner is my favorite. Cheap flights, good UI on both web and mobile, and they do a great job of figuring out the cheapest way to get somewhere if you are somewhat flexible with dates/times or flexible with where you want to go.
- Reveal hidden prices. They claim this - "We're better at finding cheap flights than anyone else— so good, United Airlines actually sued us for it". Skiplagged 2 [New version] They show hidden city ticketing trips in addition to what sites like Expedia, KAYAK, and Travelocity show. Taking a stop might save hundreds of dollar as @melaniepinola mentioned here - http://lifehacker.com/skiplagged... You can also track previous searches for changes in price. Available on iOS/Android.