I chose Nikon. And I'm proud to say that. Some chose Canon. Others chose Sony. Its all down to personal preference. We can't all go around discriminating other brands. But heck, I do it :P Anyway, going back to the topic. There are very good reasons why I became a Nikon-ian instead of a Canon-ian(sounds weird) or a Sony-ian.
1) It can practically see in the dark
Nikon DSLRs are just magnificent. They can literally see in the dark. Compared to Canon's or Sony's, the ISO performance on Nikon's are god-like. I usually shoot at ISO 800, but if I'm forced to(since I don't have an external flash and a fast prime at the current moment) shoot at high ISO's, I will. Of course, ISO 6400 will give you very noisy results but its better than Canon's ISO 6,400. Most of my night candids are shot at ISO 3,200 max.
2) Ergonomics master
Pretty gay way of saying it. To me, Nikon's are just perfect when it comes to ergonomics. Especially the higher end models, like the D7000, D300s, D700, etc. Their grip is just perfect. Should you use a pro lens like the 24-70mm f2.8 things just gets better and better. One of the main reasons why Nikon gets my vote when it comes to ergonomics is that they placed the thumb dial at the back of the camera opposed to the oddly-placed finger dial at the top of the camera. This makes one handed operations much easier on Nikon DSLRs. Buttons are placed more sensibly on the Nikon. Canon's previous layout was OK, but they've changed them to a more, weird layout(look at Canon's latest lineup of DSLRs).
3) Brilliant wireless flash system
Nikon uses this wireless flash system called Creative Lighting System(CLS). Not sure about Canon's wireless flash system, but heard that there were problems or it was just too sophisticated for rookies. For Nikon, its quite simple. First, make sure your camera and flash supports this feature - D70, D70S, D80, D90, D7000, D200, D300, D300s, D700, D3, D3x, D3s and SB600, SB700, SB800, and SB900. The D3000, D3100, D5000 and SB400 won't support this feature, sorry guys ):
4) Sharp lenses
Yes, Nikon does have a few sharp glasses. I was actually surprised by how sharp it was at the price you were paying for. The 18-55mm VR is a good example. As a kit lens for the cheaper bodies, it costs only RM400+. However, in terms of sharpness, it rules. We're not talking about build quality, or the smoothness of the bokeh here. One of the main reasons why I hate it, is because of its autofocus speed. Its so slow, it struggles to focus on my brother when he rides on his bike(yes, its very slow). I do get him focussed in shots, but rarely.
5) Compatible with lenses since 1959
Call me a Nikon fanboy, but Canon only supports lenses till 1985 - the great divide. That's when Canon decided to flush their previous system and all the lenses before it. That's when they came up with EOS(Electro-Optical System). And because Nikon didn't flush their system like what Canon did, we Nikon users get to choose from a wide variety of lenses. But do note that lenses at that time are manual focus(meaning you have to focus yourself) and you need a camera that is able to meter these lenses. The D200, D300, D700, D3, D3x, D3s will meter these lenses.
Now you have 5 more reasons why you should shoot Nikon (: