Even though I know you said you don't have a budget, there has to be somewhat. A VERY general rule of thumb is to take the maximum you are willing to spend, divide it by 3. Spend one third on the body and the remaining 2/3's on lenses. The lenses are much more important than the body. That being said, here's my $.02
1. First and foremost, don't be lured in by megapixels. Unless you are printing your photos at huge sizes there isn't much need for anything above 10. (I'll probably be bashed for that and there are reasons pros need more)
2. Canon, Nikon, Sony, and maybe 1 or 2 others are really the only brands I would look at. Canon and Nikon usually make slightly better cameras because that's all they do. And between those 2, honestly, it's all up to your preference. Both are on the forefront of technology and both are always competing against each other. The menu layout is different and the button layout is different, but that's about it.
3. Size and weight grow substantially the further up the product chain you go. So if it's going to be something you carry around all day you might want to consider that.
4. Video. Plain and simple.
Those are just a few things to look into. I use Nikon, so for my money I would look at the D5000 or the D3100. If you are willing to get a used camera, the D40x is a great place to start.
Also, there are TONS of articles geared to this decision process on the web, just do a simple search.
Good Luck!