You need to be a fair bit more specific.
1. Budget: How much do you want to spend? How much are you willing to spend?
2. Function: What focal length(s) are you thinking about?
3. Features: Do you want to shoot macro? Do you want to shoot at a fast aperture? Do you want VR? Do you want a prime, or a zoom?
4. Expectations: What do you want to get out of the new lens that you cannot do with your current lenses?
My generic response without knowing any of the above would be:
If you're looking at getting a prime lens, look at the 35mm 1.8G, 50mm 1.8G, or 85mm 1.8G. All three are good. I would lean toward the 35 or the 50 for most things. The 35mm 1.8G is the most versatile, the 50mm 1.8G is really useful for portraiture and general things, and the 85mm 1.8G is great almost purely for portraiture.
If you're looking at getting a step up in the nature/wildlife area, I would recommend the 150-600mm Contemporary (Sigma) lens. If that's too much money, the 70-300 VR (Nikon) lens is an incremental upgrade over the 55-200 by a fair margin. Tamron's offering is also worth considering, in the end I'd buy whatever you can get your hands on in a store to test in person. Other options include Tamron's 70-300 VC lens.
If you're looking at getting an ultrawide, the Nikon 10-24mm is going to perform the best on the DX body hands down. However, if that's too much money, there are other options, but the choice can get a little more complicated.