I'm always stuck (DX) looking for a basic zoom in that 17-150 range and have found all to be garbage by my persnickety standards. I have broke 3 plastic mounts in the past so the 18-105 is out, the 18-200vr is overpriced and both have enough distortion that it bugs me to no end. The 16-85vr comes close but is at 5.6 by 50mm which is way to slow (lack of bokeh) for what I want my glass to achieve. The Tamron 17-50 VC comes really close but alas it is too short as I love to shoot from the 40-100mm FX range. All of this added together, I along with many, will be left wanting endlessly forever I fear. The only option I have came up with is to go FX and get the 24-120 f4 (have not done) or just get used to swapping lenses wither either f4s, 2.8s and primes (that is what I do).
Walk around lenses have always been full of trade-offs. If you don't mind shooting at f5.6-11 they work really well. For someone like me, they should just paint them red since they are the Devils work - the details always leave me scorched.
That said all the lenses are sharp, perform extremely well and optically superior than any other brands and any previous options. Calling the "18-200 is optically inferior" is far from the truth and maybe someone got an out of alignment lens. Anyone who thinks they are soft needs to spend more time with the lenses from Sigma in this range and not compare them to the Nikkor 2.8s.
Given the price of the 18-105, it should be a no brainer to get one. Add the 70-300 and you have good overlap (which is always overlooked and is an understated need) and a hell of a walk around/travel/everything kit.
Advice: If you still feel "left wanting" - Just give in and realize you will be carrying a lot of weight for the glass you want. Don't worry you are not the only one.
While I know this is about the 18-105mm, I'd like to say a few word about the 18-135mm. I'm happy with the 18-135mm, the predecessor to the 18-105 VR. I had chosen it as an alternative to the 18-55 and 55-200 kit zooms that would have came with the D40. I've used it since the beginning of my DSLR days, which would be from 2008 till now. I'll have to admit, it does vignette a bit and purple fringes quite a bit. But I would say that it's plenty sharp and the bokeh at the long end is even good to fair.
On the way to buying a D40, I was considering between getting the D40 with the 18-135 or 18-55 dual kit lenses or even getting a D40x body only with the 18-200mm. I considered the 18-200 to be too expensive and at that point I didn't know if I would be thinking about doing photography for the long haul. The 18-135 probably has similar build to the 18-105, and it's a plastic fantastic lens. Definitely not built to withstand anything, but I'd say it's not a bad lens at all. Additionally, I've used the 18-55 and I feel that the 18-135 focuses just slightly faster than the 18-55.
Jeez, after looking at the price of an 18-200, I don't think I'd be getting it anytime soon. I've seen it at a low of around $650 to $700, and I think after the tsunami disaster automatically raised the price of it. The 70-300 is at $586 right now at B and H. $300 isn't peanuts, and I'd much rather be spending that change on a 50mm 1.8 AF-S instead. I agree with the earlier comments from JohnnyApple, the 70-300 VR is optically superb and probably pairs better with the kit lenses. On the plus side, it's also FX glass, which won't be going anywhere in the future.
Here's a sample of the bokeh. No idea what the berries are but I was surprised that there was still berries in late November.