Your best deal is to get the 55-200mm AF-S VR lens. That, along with your 18-55mm, gives you a wide 18-200mm range. Now, I have an 18-200mm AF-S VR and love it. It does take the place of two lenses, saving lens-changing time and giving me a lighter package to carry along. When I went to China in 2007, it was the only lens I brought along.
But, the rule of thumb is - the more you expect from one lens, the poorer result you will get. Think of a dedicated all-in-one tool vs a toolbox. Yes, you can do alot with that all-in-one, but a true craftsman uses different tools for each job.
Just remember this. You probably won't be able to sell the 18-55mm for very much. It's better to keep it and suppliment.
As for brands, you can use any Sigma, Tamron, Tokina, or other brand lens that has a built-in autofocus motor.
Here's a partial list for you.
http://en.wikipedia.org/wiki/List_of_Nikon_compatible_lenses_with_integrated_autofocus-motor
If you have any other questions please feel free to email me.