Advanced, high-performance Speedlights for Nikon digital SLR cameras!
Eventually you may want to get a speedlight for your new D90 and that's a great idea! I just got the SB600 and i love it. I'm still learning the best way to use it, When i get it right my photos have come out great. I use it off camera with the commander mode and boy is that fun. Here's a few links about these speedlights. You may notice i use Amazon.com a lot to show you stuff and that really is just because they have so much information and user reviews on these products it's just a great place to get it all.
Here's a little micro site tutorial from Nikon called "The world of Nikon speedlights"