What is the next lens I should buy?

I want a new lens, and I was wondering what would be a logical next step. Here's my kit so far:
-Nikon D3000 body w/18-55mm kit lens
-55-200mm Nikkor AF-S zoom lens
-50mm Nikkor 1.8G AF-S lens (primarily used on my D90-S film camera, but it fits the d3000 as well)

So, what lens should I buy next?
If your a photographer, and you have a favorite lens, I would appreciate your input!

Go for a nice macro lens and open up a whole new world of possible photos

You have almost every shooting scenario covered. If you are interested with macro, maybe that would be the next lens. If you are interested in pulling very far objects still much closer to you maybe a cheap 800mm mirror lens will do.

http://keerok-photography.blogspot.com/2011/05/lenses-so-many-of-them-there-is-no-best.html

Erm upgrade the 18-55mm kitlens with something like a Tamron 17-50 or some other lens like that with F2.8 over its full range.

Why? Lets allot of light through, meaning you can keep on shooting as it gets darker and your kit lens begins to need more aid from the camera. Also F2.8 makes that you can use the Cross Type focal points better of your camera. Those are the quickest. Also they tend to be darn sharp.

So a 17-50mm Tammy [there are also other brands] is like giving your kitlens a turbo in image quality.

Impossible to give you a good answer without knowing what you shoot.

What do you find your current lens selection to be lacking at?
There are four possible routes from here:
Add a macro lens, such as the Nikon 60mm/2.8 or a 105mm one.
Add a ultra wide angle lens such as the Nikon 10-24mm, Sigma 10-20mm or Tokina 11-16mm
Replace your standard zoom or telephoto lens with a higher quality counterpart.
Replace your standard zoom and telephoto lens with a single Nikkor 18-200mm VR