I look at Canons, Pentax, and Sonys sometimes and they have a lot of nice features but in the end it is hard to beat Nikon's very solid metering and auto-focus. I don't think the other brands measure up at these key factors. Also even though Nikon packs a lot of crap into their user interface, they do it better and less than the others. And their "cheap" cameras are better build quality than their competitors' cheap bodies.
I've had most of the DX Nikons almost and while I am out of them, my wife has a D5100 and I just got her the 16-85 "premium" consumer zoom that hopefully is a little tighter than the $100 18-55 kit zoom (which makes good photos, just feels cheap -- but nowhere near as cheap as a Canon or Sony kit zoom!).
I think the first D300 (not the later D300s) is the best value, you can find them on Fred Miranda with low milage for $750 to $800. The batteries are plentiful and inexpensive, they take all the lenses, and the finder is as good as you are ever going to get from a DX camera. But the big reason why I like them is that they have far and away the best auto-focus of any DSLR, even the full-frame D3s. The D300 is packed with AF points and they fill the frame, unlike the full frame models where the same sensors are concentrated only in the central portion of the frame. Also the tracking is phenomenal and better than anything else I've used... you can pick a running kid or critter and the camera will quickly keep up - it is amazing.
Even my old F100 has tracking but on the D300 it is fantastic!
Also the D300 is very well built and feels very solid. I used it a lot with the fine 35/1.8 AFS DX prime ($200, 50mm equiv.) and it rocks.
Other good lenses would be the newer 50/1.8 AFS G ($200) and an older AIS 24/2.8 or 24/2 ($200 to $500) - a nice conservative and not too expensive set of lightweight primes. Like Canon, Nikon is brain dead when it comes to which lenses they release - if they only had a 24/2.8 AFS DX prime that was $300 they sell a gazillion of them.
I tried the D7000 and while the sensor is supposed to be better, the build quality is more akin to a D90 than a D300. Also the menus bloated out to be nearly endless. I suspect the next D800 is going to become a bloated pig of options and video and crap loaded on....
I could use the D300 to ISO 800 for color and 1600-3200 for B&W.
If you want a lighter weight version the D90 (>$600) is pretty much the best option but the AF isn't as good. Lighter though! Same sensor as the D300.
If you want to save money and drop a couple stops of usable ISO, the D200 (>$450-500) and D80 (>$350) are fine cameras with the same sensor. I limited them to ISO 400 for color and 800 for B&W. I think the D200 is quite nice actually, it was the last of the crisp CCD sensors and it has a unique image quality that converts to B&W well. The D80 is solid but the metering can be "bright" and you have to pay attention to exposure more than usual.
I have D70 stuff in my portfolio that still holds up fine but it is hard to use it for color above ISO 400 ~ for B&W you can call noise grain and accept 800. They can be found cheap, like $200, but you can find $300 D80s and the LCD is twice as large. The D70 now feels retro whilst the D80 still feels like a contemporary camera.
It is nice to pick up a D70 though - very simple menus, 6mp files are fast to move around, it is almost like a Lomo in its simplicity compared to the latest bloatware.
The kit zoom they released with the D70 - the 18-70 AFS DX - is a nice solid inexpensive consumer zoom without faults. The newer kit zooms have VR and such but aren't built as well for the money.
I'd try to avoid the D50, D40, D60, D3000, D5000 models as they were the most consumer-price point orientated models and crippled or cheapened in someway. The current D3100, D5100 models are nice and have a lot of features but only use the AFS lenses if you want proper AF and metering. I think that is fine for the family snapshooter but not so much for someone who is going to want control.
In the end? Well never look through a full-frame camera and you'll be happy. The damn F100 ($200 35mm film) and D700 FX ($2000) don't offer much more... other than a great view. It is just hard to go back to the tiny finder afterwards. For that matter, the EVF in the newer m4/3s and Sonys, etc. is nice - I think the EVF in the cheap, venerable Panasonic G1 is in a lot of ways better than that of a DX optical finder. That's why the D5100 with the swinging tilting LCD and Live View is a more viable camera for my wife (and for me to grab).
So basically I pontificated for 30 minutes only to arrive at the conclusion that the DX APS finders suck... ;-/
