Bub,
As has been mentioned previously, the current entry level offerings from canon/nikon are very capable - which is better is very much a matter of opinion, and realistically, they will all take fantastic photos.
As has been stated, extension tubes with the right lens will give you a macro ability, but the lens correction will not be ideal, so quality will be somewhat compromised. It really does depend on how macro you mean, and what quality of result you are after.
Just as an example, the canon standard kit lens for cropped cameras, the 18-55 IS, has a magnification of 0.34x. Basically the sensor image is 1/3rd of the size of the item you are photographing. If this is enough magnification depends on the application. General purpose lenses are optimised for inifinity focus, and will have softness and chromatic problems at close distances. Again, this may or may not be a problem depending on application.
So my advice? Get a standard canon/nikon intro camera setup, with their standard kit zoom, and see if the macro ability is good enough. Get extension tubes first to give you more macro, or if you decide you want to go properly macro, a nice macro telephoto, maybe the tamron 90mm macro which is generally considered a fine optic.
Oh, and one other thing, canon do a MP E 65mm macro lens which is a very odd beast. It goes from 1x to 5x magnification, so it's really a microscope in canon EF lens mount. It costs lots though, but if that's your thing, worth thinking about.
Cesare