IMO you can't go wrong with Canon or Nikon. As stve says, if you're a beginner it's best to go for the bottom end of the price range. Mind you even the top models have an Auto function.
Also I concur with gogreen. The glass is crucial. You can get away with a good lens on a beginners body but you would be wasting your time putting a cheap lens on any camera.
I suggest you do some research before buying, both online and in review magazines.
I have a Canon 40D (now superseded by the 60D) and Canon lenses and I'm very happy with it. This camera is at the top end of the "consumer" range.
"Pro" cameras tend to have "full frame" sensors. They are the same size as a 35mm film frame. This gives greater quality with the same number of pixels as a APS-C sensor (as found on consumer cameras) purely because it is bigger.
The other thing you pay your thousands for is an extremely sturdy body, weatherproofing etc., which is suited to the many conditions photojournalists etc have to face.
Don't get hung up on how many megapixels a model has. More is not necessarily better.
Basically-read the reviews in your price range and then go in a shop and handle the camera.