The main differences between a male and female will be the pouch (opening on the lower abdomen that a female can keep very tightly closed, or relaxed and open, depending on how comfortable she is at any given time) and the scrotum/testes (which, just as with most male animals, the glider can either keep tight against his body, or let really dangle low, depending on the temperature).
A male will also occasionally (or frequently, depending on the male) show off a bifurcated penis which looks like 2 very thin, long, red worms that are connected at the base and come out of the cloaca.
As males and females mature, there are a couple of other physical appearance traits an intact male will show - they will (usually) get a 'bald spot' on their chest and the top of their head. Depending on the male, these can be very large, or not very noticeable. They can be stained very yellow around their bald spots or no difference in color at all.
These bald spots appear over scent glands and occur because of the increased production of oils from the gland that slick down the fur in that area. If they do not have a cage mate to help them keep clean, the oils can sometimes build up and make the area look crusty. The more a male scents (his cage, this cage mate(s) and things in his cage) the more likely you will see a larger scent gland bald spot and possible staining around the gland.