The Nikon SB-28 flash was the top-shelf flash back when the F5 and F100 were available new. I've used the SB-28 with my F100 with flawless results and now I use it with my D90 with flawless results. On the D90, the SB-28 is manual only, but with "chimping" I actually get even better results than I get with my F100. You just have to recognize what the lcd monitor on the D90 is showing you; I can usually dial down the flash to improve the shadows enough to show detail. Settings on it include 1/1 to 1/64 on manual setting and if you shoot film +/- 3 stops exposure compensation in TTL mode.
I get a Nikon flash, save money, and get high-end quality by choosing the SB-28 over an SB-600 or SB-700. Unfortunately, it seems they are no longer dropping in price and are actually becoming more expensive. If you can find one at a good price, get one. You won't regret it.