There are really only two models in current production. Current production is essentially the third revision: "E". There are three color variations.
SW9VE
SW: Smith and Wesson
9: 9mm
V: Value
E: enhanced
SW40VE
40: .40 S&W
If you see a "G", it's green. (SW9GVE)
The Allied forces model has a black slide, but the same model markings.
http://www.smith-wesson.com/we...r1=EQUAL&isFirearm=Y
And before you ask, no you can't switch parts between the 9 and 40 and have 2 calibers on one gun: the frames and magazines are different.