Nice buy! I'm just getting used to my new d90 as well.
Mine came with the 18-105 kit lens too, it has worked great for me but I'm also looking at getting that 50mm f/1.8D, mainly for lower light situations, and the ability to get more creative with bokeh at the wider aperture. If I had the money I'd go with the Nikon 50mm f/1.4G - or the Sigma version of it...
Regarding "after-market" (non-nikon) lenses, I dont see a problem as long as you do your homework on the lens first, I always check out kenrockwell.com for lens reviews and comparisons, very in-depth and non-bias.
Cheers and good luck with the camera! I'll keep my eye out for your future pic posts