I want to do that too, buy the 18-105 mm + 70-300mm lens, but I am looking to save some money. I could do a d90 and then those two lenses but I would like to buy the latest and greatest of what I can afford.
I guess I will have to just settle with the kit.
1. Search Flickr for the lenses you are interested in, click on "Slide Show", and view the various pictures, taking into account the various PP techniques that each user may use. Make sure that you un-check the "Embiggen things to fit screen" box.
2. Take a look at the Tamron 18-270 VC PZD either on Flickr or at your local shop (where it would be returnable); if it's sharp enough for you, it will be a whole lot more convenient. I just got back from Washington DC with my 18-105 VR, Nikon 35mm 1.8, and Tamron 70-300mm VC. We did a lot of walking, and the one lens solution would have been very nice.
3. The 18-200 VR on Flickr (use the search function in Flickr) shows a lot of very nice, sharp pictures. Customer satisfaction on this lens is very high.
4. I agree with those who say "get a 70-300". The Tamron VC can be gotten for around $400 after rebates, and it's basically as good as the Nikon 70-300 VR--some things are even better (Image Stabilization and bokeh; reviews are mixed on which lens is sharper past 200mm, which I attribute to sample variation). Having said that, I rate the Nikon as slightly better because it's color reproduction is more pleasing to my tastes. I bought the Tamron only because the slight improvement in color wasn't worth the $189 price difference at the time. Both the Tamron and the Nikon are very good.
5. I also have the 50mm 1.8, and I would recommend the 35mm over the 50. The 50mm is just too close for most of the shots I take, even on vacation.
6. The 18-105 VR is great, but it has plastic flanges that you need to be careful with (mine broke because someone wasn't careful; I got it fixed w/in 24hrs, though). Yes, it has distortion, but most people are able to correct it in PP.
Hope this helps,
Steve