I was thinking of getting a new lens but now I am thinking that maybe I should upgrade the D90 to a D7000 (they are $900 until Dec 15th at BH and other places) instead. I currently have D90 and Nikon 35mm f/1.8, Nikon 40mm f/2.8 macro, Nikon 18-200 f/3.5-5.6 VRII for everyday lenses.
Here are my options.
1) Upgrade D90 to D7000
2) Get the Sigma 17-50 f/2.8 and use this instead of the 35mm f/1.8 as my everyday lens
3) Do nothing and stick with D90 + 35mm as my everyday lens