Yeah the Nikon 18-200mm is a must for most of the DSLR owners. I know its pricey but the quality is great. Gotta love the VR function and say goodbye to my tripods. If you are in tight budget, like wlcling said, go for those but man, shooting at 200mm without VR is headache 

If you're on a budget I'd suggest the cheap and excellent 18-55mm instead. If you need to go longer, add the 70-300mm G. You'll lose convenience, but the pair combined probably weighs less then the 18-200mm VR and costs only a fraction as much. Picture quality will be the same most of the time. Cameras and lenses have little to do with the quality of your pictures. Dollar for dollar these two lenses are better than the 18-200mm VR. All these lenses have great image quality used properly. The 18-200mm adds a new level of flexibility.

One consideration for everyone: something with a shallow DOF does not necessarily have a nice bokeh. If all you care is about being able to use a faster shutter speed, then any 1.8/2.8 lens is of no problem. But if you want a shallow DOF with the bokeh to be smooth circles (instead of pentagons or hexagons), then the number of aperture blades starts to play a role...