If you can hold out until March, there could be some newer stuff on the horizon. That said, I'm skeptical that it will be a D90 successor. For a while, the D90 and the D5000 were way to close in price point and functionality to make people want to buy a D5000. \
The two obvious solutions to that problem would be to introduce an updated D90 with better features at a higher price point, or cut the price on the D5000 to make it a more attractive option.
It appears they went with the latter. So I expect the D90 to be the High End consumer cam for the next 6 months +. If you can find a good deal on a D300 go for it. Otherwise I'd go D300s. Its got some subtle feature enhancements that make it worth it. I also like the option on storage media (CF vs. SD cards).
If you are after a photography degree, then I'd go ahead and shoot for the D300s. It will serve you well for a long time. Its probably all the DX camera you will need for years to come.