Don't spend the money on upgrade to D90. The D90's are "better" but you are never going to notice the benefits unless you are a pro sports photographer.
Almost every Nikkor / Nikon lens is going to be better than the (cheaper) other brands. If you are shooting in full manual exposure modes (which you should be for almost everything, and if you are not, you should practice and learn how to) a lens that does not have the aperture change when you zoom in and out is really valuable. Before digital, this was pretty critical; but with digital its not so much anymore. You should always shoot in RAW, and you can easily fix one stop exposure mistakes on computer.
A fast 2.8 lens is really nice to have, but in fact, what I have found with the Digital cameras is that because of the smaller sensor (compared to film plane) if you are shooting pictures wide open (at 2.8) the DOF (depth of field) is so narrow that you are rarely going to need or want such a fast lens, particularly in long lenses (200mm +). One good thing, tho, about fast lenses is that in lower light you can see the subject better because when looking through the viewfinder it is letting in max light, regardless of aperture setting.
So... current gear looks pretty good as is.
If you take lots of pics inside house (family pics, get together's, etc) ... and you want to really have some fun, get yourself a SECOND flash, with a little stand and flash trigger device - so you can setup the second flash in the room to backlight, rear fill, or "hair light" subjects. Once you get the hang of it.. it can be really easy to do and produce much, much, better photos. Remember, in photography, LIGHT IS EVERYTHING!!!