Every DSLR is going to be good, but each has its own quirks. There are more Canon shooters than anything else, so if you are going to want to share with friends, see what they have. Canon likely has the biggest lineup of new lenses as well. The second most popular is Nikon, but as was pointed out, if you go with the base model you have some lens limitations. Unfortunately, the best bang for the buck low light lens (50mm f/1.8) is one of them. I shoot a Pentax K100D. The benefit of Pentax (as well as Sony, the new Olympus models, and Samsung) is that they have in body image stabilization on the current models. That makes any lens you mount have IS. With Canon and Nikon you have it in lens, which makes the lens cost more. The in lens system is probably a little better, but the body based system is still very effective. Samsungs are clones of the Pentax, but not really seen much in the US. The Olympus has a different type of sensor that is an upside to some and a downside to others. Instead of affecting the focal length of a lens by a facor of 1.5x-1.6x for the consumer level models from the other brands, they have a 2x factor. That means that a 14-40mm lens essentially acts like a 28-80mm. It is good if you want to do a lot of telephoto end shooting, but not that great if you want wider than the effective 28mm. It also makes the depth of field(in focus area of a shot) larger. That is usually a plus for someone making the jump from a p&s b/c they have a very large DOF. On the other hand, many DSLR users like to make the DOF really small to blur the background. It can be done with the Oly, but not as easily and not by the same amount. They also have smaller sensors which usually leads to a little more image noise at high ISOs. They seem to be getting it more under control with software in the newer models, but that can be at the cost of image sharpness.
Another very important thing to consider is the feel in your hands. The entry level Canon and Nikon models are on the small side, so good if you have small hands, but bad if you have larger hands. The entry level Pentax and Samsung models are a little larger.
Not to overwhelm you with info, but while I am on a roll, you really need to think hard about your upgrade path and what lenses you will want now and in the future. If you are going to go with C or N and the kit lens (basic 18-55mm) then be aware that the optical and build quality of that lens is intentionally not as good as their more expensive models. They want you to upgrade. The other brands are competing for market share more and typically offer a better quality kit lens. I am still using my Pentax one and am very happy with it in results and build quality. Also, if you think you might go towards pro level gear in the relatively near future, then stick to C&N as the other brands might not have as much to offer and/or might not even be around in ten years. I personally believe that all the current companies will still be around and offering pro gear b/c the market is continuing to grow, but you never know.
Kevin
