I just took the plunge for the Nikkor 18-200mm VR and I am pretty sure it will stay on the D50 for a good while. I wasn't sure about this until I had a chance to see VR in action but it is the real deal. The 18-200 covers just about everything you need Landscapes to portraits.

Purely on the basis of focal length, the logical lens would be a 10-20mm or 12-24. It nicely fills the wide-angle gap that the 28-300mm misses.

I have spent the past few weeks somewhat in parallel with you. Not just for glass but for the whole system. I am pretty discouraged with what I have found. I will share it in case it is in sync with what you are finding.

I must admit my bias - the 18mm equivalent lens has been my preference for a large percentage of my shooting. The equivalent focal length on a D80 would be 12mm. I did a similar trip with film, and most was shot with the equivalent to an 18mm focal length on a 6x10 medium-format superwide camera. Were I to do the same journey with digital, I would probably opt for the 12-24mm Nikkor.

Sigma glass has a decent reputation, but the lens mounts have been where they have traditionally skimped to keep down price. Same with the rest of the third party vendors. I have some third-party lenses, but they tend to be for occasional use, and I keep a jeweler's screwdriver in my working bag. If I do convince myself to get a D200, the 12-24 would be my main lens, so I would choose the Nikkor.

I would bring the 28-300 if I had it, but probably would never use it, unless there was some small critter that I wanted to photograph.

Indoors is problematic with zooms. Much of my shooting with film was necessarily indoors with ambient light, and all my Nikon glass was very fast primes. I handled a D200 but with a f-4.0 zoom, and the view is really depressingly dark in the camera shop. F-2.8 is about as fast as zooms get, and that would still present a pretty dim view. This is one of the main reasons I am hesitating to buy a dSLR. My primes are all manual lenses and while they would work on the D200, it is with substantial compromises. Of course, none are specifically designed to work optimally with a sensor.

About the most viable lens I have found for indoor shooting is the Sigma 30mm f-1.4, however, it is a bit too long for my taste. Nikon does make some primes in the right range for focal length, but they are all in the f-2.8 to f-3.5 range - dark again. A lens of 12 to 15mm at f-1.4 would get my full attention.

So for an indoor lens I have no recommendation other than perhaps the Sigma 30mm. It is roughly equivalent to a normal lens on a 35mm camera and certainly has an aperture appropriate for indoor use.

So I can only speak from my own viewpoint, since everyone's photographic workflow is unique to them. If the glass I wanted existed, the authorized Nikon dealer is less than 300 yards from my back door, and I would have the D200 in a moment. However, with a 12-24mm lens in addition to your present lens, you are pretty much equipped for anything - as far as coverage goes.

I would use the 20mm f2.8 for an everyday lens, or at least I would if I carried the camera around.

It's 30mm equivelent (thought not wide enough) is about as wide, small, light and fast as you're going to get in that price range.