Ok- I don't use any of those cameras, but I do have something useful for you. I have no idea what Nikon has on offer in comparision, but IMHO you will absolutely, madly and passionately adore the combination of the 5D and the 24-105mm f/4 L IS. I have the 24-105 and it is awesome. Built tough, very good IS, brilliant colour and contrast, and a nice, solid size. It's only f/4, but the 3-stop (I think?) IS makes up for this nicely, in my experience. So, you can't go wrong with a 5D and a 24-105, especially if you pick up a used one, as they are super cheap now that the 5D MkII is out (like $1500).

If I was buying one camera and one lens, that would be it. But on the other hand, I'd go cheaper and buy two lenses- a 40D, a 17-40/4 and a 70-200/4. But that's me :-)