From Boeing, the B737NGs have the following maximum capacity:
B737-600: 130 seats,
B737-700: 148 seats,
B737-800: 189 seats,
B737-900: 189 seats, (due to same exit door config. as the -800)
B737-900ER: 215 seats (additional pair of exit doors vs -800/900)
I believe the -900 is only operated in Europe by KLM (mixed c/y configuration) and is now out of production. Only the -900ERs are being produced.