equipment recommendation - D5100 or D90 ? Which one to buy as the first DSLR?

I am planning to buy my first DSLR camera and have pinned down on Nikon. However, I am not able to make up my mind between the Nikon D90 and Nikon D5100. While D90 is more expensive, I am not sure if the additional $250 are worth it ? Any suggestions ?