USA
ATA/Southwest (Chicago)
AirTran (Atlanta)
America West (Phoenix, Vegas)
Frontier (Denver, LA)
jetBlue (NYC/JFK, Long Beach)
Midwest Airlines Saver (Milwaukee, Kansas City)
Song [Delta] (Boston, NYC, Orlando, Ft. Lauderdale)
Southwest (dozens, especially Phoenix, Vegas, BWI)
Spirit (Detroit, Ft. Lauderdale, Chicago)
Sun Country (Minneapolis, Vegas, Laughlin)
Ted [United] (Denver)
USA3000 (BWI, Ft. Myers, St. Pete)

CANADA
CanJet (Montréal, Toronto)
Jazz [Air Canada] (Toronto, Montréal, Calgary, Vancouver)
WestJet (Toronto, Calgary, Winnipeg, Edmonton)