In perusing Bill Harm's registration web-site, and from my personal observations at MSY, there are a number of other suffixes on SW aircraft, especially on the -700's.
They include N700GS, N711HK, N714CB, N737JW, N738CB, N761RR, N777QC, and one to be delivered shortly as N797MX (all these are -700's).
N702ML is still around (as a -200).
I do believe that some of the 737's picked up from American are still around.
Tom in NO (at MSY)
"The criminal ineptitude makes you furious"-Bruce Springsteen, after seeing firsthand the damage from Hurricane Katrina