Low-Cost Airlines in United States of America
AirTran
Flights from many cities in the Eastern USA
Allegiant Air
Flights between Las Vegas and several East Coast cities
American Trans Air (ATA)
Flights from many cities all over the USA
JetBlue Airways Latest
Flights from New York - JFK Airport to 30 US destinations
Midwest Express
Flights from many cities all over the USA
Southwest Airlines
Flights from many cities all over the USA
Spirit Airlines
Flights operate mainly between Florida and Chicago, Detroit, New York
Ted
Flights from Northeast USA to Southeast and Western USA
USA 3000 Airlines
Flights from Midwest and Northeastern USA to Florida, Cancun, Dom.Rep.
Reference:  http://www.discountairfares.com/lcostusa.htm