D5000 and D90

[Exiztence]

Like wannabephotographer said, I'd wait a little for the D90 replacement. If that's going to be a far better camera than the D90, you'll advance a good deal in camera quality, which is worth the money.

Otherwise, if you like the weight of your current camera and plan to use AF-S lenses only, I'd go for a D5000. The D5000 and D90 don't differ in image quality. (If you won't use the added functionalities of the D90).