Los Cabos-Cabo San Lucas is served by most major airlines...and some not so major, with plenty of direct flights from the U.S./Canadian cities coast to coast and more being added every season. My Canadian clients are ecstatic about the new non-stop routes on WestJet from Calgary and Kelowna.
Commercial jet service to San José del Cabo International Airport (SJD) is provided by Alaska, American, Continental, Delta, United, Northwest, Frontier, US Airways, Mexicana, Aero Mexico and Aero California... and if you are in the San Diego area, Volaris out of Tijuana which has a shuttle service out of downtown San Diego and has great prices.
There are non-stop flights from San Diego, Los Angeles, Ontario, San Jose (CA), San Francisco, Seattle, Salt Lake City, Denver, Chicago, Atlanta, Minneapolis, Phoenix, Houston, Dallas, and Las Vegas into Los Cabos...and now Westjet flies from Calgary and I believe Kelowna, Canada.
Connecting flights are available from Sacramento, Portland, Detroit, Boston, Newark, New York, Tulsa, Oklahoma City, Saint Louis, Miami, Albuquerque, Austin, Vancouver, Calgary and Toronto.
Airline Telephone Number Website
Alaska Airlines 800.252.7522
local: 146-5380
US Airways 800.428.4322 www.usairways.com (formerly America West) In my opinion, best value.
American Airlines 800.433.7300
local: 146-5300
www.aa.com Probably the most expensive especially out of Dallas!!!
Continental Airlines 800.231.0856
local: 146-5040
Delta Airlines 800.221.1212 www.delta.com
Mexicana Airines 800.366.5400 
local: 146-5001/2
www.mexicana.com out of business.  I'm leaving this for when they return.
United Airlines 800.241.6522 www.united.com
West Jet 877.952.0100 www.westjet.com
Frontier Airlines 800.432.1359 www.frontierairlines.com (Please check their Mexico schedule according to season)
Volaris 866.988.3527 www.volaris.com.mx   Great if you are living in San Diego County!


For Aero Calafia, Aero Mexico, and Aero California: if you are in Mexico I suggest contacting a travel agent. Their websites are difficult to navigate. Hit your translate button unless you are bilingual.