I use the Sigma 10-20 on my D5100. There are 2 of them, I have the slower and cheaper one (4-5.6). It works great for car shows, closeups, etc.
You should also look at a good telephoto. Lost of shots are better from long range, and the telephoto compresses the photo well. Look at the Sigma 70-200 2.8 OS, and the Nikkors (80-200 2.8 AF-S) and (70-200 2.8 VR)