Scotts Cheap Flights - You can save thousands on out of country flights if you are willing to book right away! Please see THIS POST for more details on this!
Allegiant Flexible on when and where they will save you hundreds!
Frontier KIDS FLY FREE - yup, you're reading right! After a one time charge of $50 dollars your kids can fly for free, up to 12 years old. Please read THIS POST for more info on how it work.
Southwest - Build up airline miles and you can get flights for cheap or sometimes free! For more details on these tips see THIS POST
For tips with flying with kids see THIS POST