Either Nikon or Canon will do, both have comparable models and performance. I shoot with Canon, my brother shoots with NIkon ... same s**t different pile as both systems can do (mostly) what the other does.
The first big question is what do you want to do with your DSLR? Alot of people get lured into a DSLR only to have it sit at home because they no longer want to lug the "gear" around after the novelty wears off.
The first thing to look at is what lenses each system (Canon/Nikon) has to offer that'll fit your purpose. Buying a body is usually on the cheaper side of things, the glass (lenses) is normally where the real costs come in. Since you mentioned low light shooting, good, fast lenses are not cheap. As an example, a EFS 17-55 f2.8 IS for a Canon crop body will set you back a grand, tele-zoom for low light $1300 (almost double that if you want IS on it).
I'm not trying to scare you off, seriously, photography is alot of fun but like so many other hobbies it can be expensive when you want good results. Part of getting good results are from the hardware, having the right gear for the shot matters. The biggest part is coming from you, understanding light, DOF and handling your gear correctly are huge factors.
Steve