Here's a quick and handy list of airlines that matter. Most, if not all, will have seasonal and regional specials posted on their individual sites. Just look for "Special Offers," "Hot Deals" or something similar on the mainpages to start your comparison shopping for the best deals.
Airtran Airlines
tel. 800/247-8726
www.airtran.com
Alaska Airlines
tel. 800/252-7522
www.alaskaair.com
American Airlines
tel. 800/433-7300
www.aa.com
American Trans Air
tel. 800/225-2995
www.ata.com
America West Airlines
tel. 800/235-9292
www.americawest.com
Cape Air
tel. 800/352-0714
www.flycapeair.com
Continental Airlines
tel. 800/525-0280
www.continental.com
Delta Air Lines
tel. 800/221-1212
www.delta.com
Frontier Airlines
tel. 800/432-1359
www.frontierairlines.com
JetBlue Airlines
tel. 800/538-2583
www.jetblue.com
Midwest Express
tel. 800/452-2022
www.midwestexpress.com
Northwest Airlines
tel. 800/225-2525
www.nwa.com
Pan American Airways
tel. 800/359-7262
www.flypanam.com
Song
tel. 800/359-7664
www.flysong.com
Southwest Airlines
tel. 800/435-9792
www.southwest.com
Spirit Airlines
tel. 800/772-7117
www.spiritair.com
Ted Airlines
tel. 800/225-5833
www.flyted.com
United Airlines
tel. 800/241-6522
www.united.com
US Airways
tel. 800/428-4322
www.usairways.com