Southwest Airlines is our top choice, simply because of their free bags policy and open seating (you just have to remember to check in right at the 24 hours prior to your flight to get a decent boarding group). They also offer a flexible cancellation where you can get credit to be used by the date of when you booked your original ticket.
Spirit Airlines: yeah, they get a bad rap, and mostly well deserved for all of their nickel and diming. But if you know what you are getting into and can plan accordingly, you can travel for pretty cheap. Case in point: a mid-week, 24-hours in Vegas flight for about $75 round trip. Lisa and I also flew to San Diego round trip for a total of $200, just $100 each. Spirit can be pretty cramped and passengers and employees grumpy, but if you can handle a couple of hours of discomfort to save a little money, you can actually save quite a big bit of money — just remember to fill your own water bottle prior to boarding so you don’t pay an exorbitant amount for water! Tips – sign up for their email club and they will often send out discount codes for ticket purchases. You can also save up to $17.99 per one-way flight on their “Passenger Service Fee” if you purchase your ticket directly with a Spirit team member at the airport.
Frontier Airlines: another no-frills carrier, this one based out of Denver, and offering great deals to all parts of the country if you can deal with their additional charges for seat selection, baggage, in-cabin refreshments, etc. They have a special fare club “Discount Den” that requires a $49.99 yearly fee for even more savings.
Alaska Airlines: we keep at least one Bank of America Alaska Airlines Visa Signature credit card to take advantage of their $121 annual companion fare. The annual fee is $75, but in addition to the companion fare you also receive a free checked bag for yourself and other passengers.