Hi
Just my two cents but I agree with Fox Racer2 the Sigma is a great lens. I have it on my D90 and love it terrific all around shooter. Nice size not to heavy and great results for near half the price of the Nikon. I was lucky and found a used one in new condition for $200.00 you will not go wrong with this one.
Will definitely check it out. What do you think of getting a combo of 18-105 and 70-300?