Shorty6049 is dead on...this is a poor place to ask. Everyone will give you their respective brand to try out. I suggest you go to a local shop and try out all of the camera bodies you are interested in. That was the deciding factor for me and probably a lot of other users. Its not a good camera if it doesn't feel good in your hands. Remember, YOU will be the one using it. How does the menus layout, are they easy to navigate, button locations, etc. are all things to consider. Ease of use is paramount in this respect since as you advance you will need to change focal points, aperature, ISO practically on the fly without having to scoll through endless munues to do so.
All the top brands are practically the same as far as technology is concerned. All about the same megapixels, basic features, lens line-up etc. You have to decide which feature you rely on most. Each brand will have strengths and shortcomings. This is where your research will have to guide you. Do you want a beginner consumer brand model D40, d40X, Rebel Xti, etc or a pro-sumer model D200, D80, 5D, 30D. Budget will become an issue as you want more features, higher image quality, etc. Decide on what your needs are and go from there. What are you planning to shoot? Wildlife, weddings, sports? All things to consider as this will come into play as you set your priorities, future lens purchases, etc.
A lot to digest, but your research and time spent now will pay off in the end. Just take your time and make the purchase that you are happy with.