Canon or Nixon

you might want to check reviews of the niKon D80 in the niKon forum, and see what others have to say. Additionally, you could compare it with reviews of the Canon 40D and see what the similarities(and differences are). Since this is the Canon forum, I doubt if people would have much(if any)experience with Nikon's digital bodies.

The big difference between Canon and Nikon is feel. Overall both make great cameras. I would suggest you try both out and see what feels better in your hands. Nobody can tell you which is better for you.

Any modern dSLR from any manufacturer will be more than sufficient for beginner's photography -- and you already made a wise decision to stay away from entry-level gear. When it comes down to Canon vs. Nikon I prefer the former, because of the better backwards-compatibility of adapted lenses, less expensive full-frame option (used 5D) and plentiful and inexpensive gear on the used market. Nikon only offers slightly better ergonomics/design and a more sensible flash technology.

But why not Pentax, Sony or Olympus? Just because Canon & Nikon spend more on their marketing? CaNik lack in-body stabilization which is a mayor drawback if you prefer prime lenses (like that 30mm). They also offer only very few APS-C dedicated primes.

If I do get the Canon I would, most likely purchase the Sigma 30/1.4 lens (it was recommended to me by the re view on photo.net that I read) but which lens should I purchase for the Nixon if I decide to get that instead?

Uh, the SigMa 30mm f/1.4 comes in all kinds of mounts... Nikon, Canon, Pentax, Olympus etc.

Canon or Nikon. Both are awesome and very capable cameras. You can't go wrong.

By all means get yourself a Sigma 30/1.4, but I suggest also picking up a kit zoom lens. Both Nikon and Canon offer kit lenses that are excellent value when purchased with the camera body. The prime and the zoom will have different creative purposes.

If you're interested in time exposures of car lights, you'll need a tripod and cable release.

you'll need a tripod and cable release.

...or a tripod and mirror-lock plus self-timer. Cable releases are not needed anymore, Arie.

As others have pointed out, it is hard to go wrong with either camera. Picking a camera is more than just picking a body however. You are picking a system: bodies, flashes, lenses and even third party support and after market support. These are the reasons I would stay with Nikon or Canon (don't get me wrong, I would love to play with the Pentax but I don't have unlimited funds!). I would ponder that decision more than just a single body decision.

Between the Canon and Nikon, I would choose Nikon. Between the 40D and the D80, I would choose the 40D. I would choose the 40D because I need the high ISO the CMOS chip in the 40D can provide. The Nikon D80 uses a CCD chip which will produce more noise at ISO 800 and above. However, the new D5000 and the D90 use a CMOS chip for lower noise now.

A refubished Canon EOS 30D or a Nikon D200 -- still available, I think -- might be worth looking at too. They were great cameras a year ago and still are. And of course Pentax. Their new K7 should send the price of the very able K20D in a positive direction.

Remember, the Canon 40D is a step above the Nikon D80. The D80 is on the same level as the Rebel XTi. They came out at the same time and was direct competitors. The 40D is a prosumer level camera. Wise to go ahead and step up first. The Nikon equivilent of the 40D is the D300. Both are great cameras. Just play with them and see which fits you best. Neither will hold you back. The more you like your camera the quicker you will learn. So see which feels better, which allows you to find menu functions easier. The one that makes the most since. Research real good, cause once you buy into the system, its not wise to switch from cost standpoint.

The Nikon equivalent of the 40D is the D300

I respectively disagree. Nikon doesn't have an equivalent to the 40D, although besides the CMOS vs CCD thing, I would say the D80 is darn close. The Nikon D90 would be the equivalent to the 50D. The Nikon D300 is in another league which Canon doesn't have an equivalent too, except perhaps the 1D Mark II/III.