While doing research for a Nikon 50mm lens, I found out that Nikon offers two types of lenses, the G and D. I found this forum discussing in detail the differences between the two types.
Essentially the G is the cheaper one of the two since it’s made of cheaper plastic. The G also doesn’t come with an aperture ring. You’ll have to set the aperture settings in your camera’s body. This means, you can’t use the G on older cameras.
I’ve been interested in acquiring a 50mm prime lens to go with my D90 camera. A 50mm lens, I think, is ideally suited for portraits, low light and bookeh photography. Speaking of forums, Dpreview is still one of my favorites. Although, I’m not a frequent visitor.