Ideally, for shooting architecture you need a camera with a bellows or perspective control. Nikon has a couple of perspective control (tilt and shift) lenses for their SLRs. I think one is a 35mm and the other an 85mm. I've not used either one so can't really speak to how effective they are, but the idea is that they will resolve the issue of "keystoning." (This is where the building looks narrower at the top than at the bottom because of the perspective from which you're shooting -- ie, ground level. The more you need to point the camera and lens upwards,the more severe will be the keystoning.) At the very least, yes, you would need a very wide-angle lens for shooting architecture, too, and there you're looking at the 12-24mm zoom or the 14mm prime (the latter having less distortion). The 10.5 DX is a delightful fisheye lens and can be used to shoot architecture, but then you need to "defish" it in Nikon Capture, NX or some other software in order to straighten out the perspective and get rid of the fisheye look.
And, yes, as has been mentioned, to shoot architecture really well and correctly, you also will need to use a tripod. Hand-held just doesn't cut the mustard. Why? Because of the depth-of field. In order to have all parts of the building in correct focus, you need to use a fairly stopped-down aperture, preferably f/22 or f/32. This is going to have an impact on your shutter speed and so a tripod really is a necessity, even on a bright day. While, sure, you can kick up the ISO, that's going to bring excessive noise into the image and you really don't want that.
I suppose at this point, as ChrisA noted, we should be asking, just exactly what do you mean by "wearing a camera around my neck all day and shooting architecture..."?? Tourist-type activities? Shooting buildings on assignment for an architectural firm or their clients or some other agencies? Obviously if you're thinking in terms of having a D80 around your neck as you do the tourist bit through various cities and such, shooting beautiful buildings as you see them, that is very different from shooting a particular building for a client. Keystoning may not be a big deal for a tourist, but it definitely is a no-no for a client who has a particular need to have the building accurately represented! Say that indeed it's the first situation (which is what I'm thinking is the case here)....a D80 and the 18-135 kit lens or the 18-200 VR lens would be just dandy. If you need to go wider, the 12-24mm will do admirably (the 14mm is pretty expensive, not a lens for the casual shooter).
Oh -- in answer to your other questions.... I'm a Nikon shooter, have been for many years. I started out with a Nikon N90 SLR back in the day, having "graduated" from various Minoltas and such. After going through a period of shooting with different Coolpixes once I got into digital imaging, I eventually bought the Nikon D70. That was followed by the D200 in December of 2005. As Chris A brings up, the bottom line here is that the camera bodies are not as important, though, as the lenses. I have amassed a rather extensive collection of Nikkor lenses which will go with me through the years as I move on to other Nikon camera bodies.... While I dearly love my D200 right now, I know that in the next two or three years Nikon will bring out some other new camera body which will be irresistible....and just as I've moved on from the D70 one day I will also move on from the D200, but my lenses will be going with me. Today I can slip my 70-200mm VR on to a D50, a D70, a D70s, a D80, a D200, a D2X, a D2Xs, a D2Hs.....not to mention all of Nikon's older generation of digital bodies and film bodies. That's pretty cool. What's even cooler is that in a year or two or three I'll be able to slip my same lens on to a new Nikon body.....
The D80 is a very nice little camera and it has apparently melded together many of the features from the D70/D70s, the D50 and the D200, so that for the price, it's a pretty darned good deal. If I were beginning to shop for a DSLR I wouldn't hesitate to snap up a D80.
Most important factor here, though, is how the camera feels in your hands. It's extremely important to have a camera which feels right to you, feels intuitive to you. Before you purchase any camera, please hold them all and play with their various features and see what seems right for you. That, in combination with a system which offers plenty of choices in lenses, is where you need to put your money.
