I'd have to respectfully disagree with nighthawk on this one, but only due to my own experience. I don't have any experience with Pentax or Olympus--but I know that you cannot go wrong with a Canon or a Nikon. They're the number one sellers for a reason. I don't know what your photographic experience is, but I'd bet almost anyone would be happy with a 20D. I have a good friend who owned and operated a very successful home-grown photography service (marketed to kids up through high-school sports teams) and he shot everything with a 10D. His pictures are of the upmost quality and I'd say professional without hesitation.

I currently with shoot with an XTi eos that I bought new off ebay a couple years ago. It is a couple steps down from the 20D, but I absolutely love it. I've shot portraits, engagement pictures, 2 weddings and it does great for that. I've also shot a lot of landscapes and various other things, but I don't yet have a great lens for that. I've had it down two very dirty and dusty caves in Utah and after it's a tough camera. I haven't tested it in water yet and don't ever plan on it, but...you get my point. Depending on the quality of lens you're getting with the camera I'd imagine paying between $800-$1400. I know that is a broad range, but it really depends on the quality of the lens you're getting with it. If you can get it for $850 or less I'd definitely buy it.

Just for fun, here are a few pictures with it. Just keep in mind the 20D will probably produce better quality images.