As stated above, when you buy D-SLR, you are buying into the whole system. You need to evaluate the whole system. You may be a newbie for now, but you may become a serious amateur and then a semi-pro, maybe even a pro one day. So you should consider a system that can allow you to grow and upgrade. Overall Canon and Nikon offer the best selections, and can satisfy most, if not all, your photographic needs, but at a price of course. Pentax is less expensive and still has a good selection (though the quality is not as good as Canon and Nikon).
The problem with Sony is that you don't know how its next D-SLR will be like. The first one is basically a make-over of the Minolta's Maxxum 5D, not the work of Sony. The lenses are also makeover of the Minolta's old lines of lenses. But Carl Zeiss is making some top quality lenses for the A100 and future Sony D-SLR. Problem is that Carl Zeiss lenses are more expensive than Canon and Nikon. The savings you get from the in-camera stabilization will be gone with one Carl Zeiss lens. For example, the Carl Zeiss 70-200mm f/2.8 G lens (without stabilization) costs $2400 whereas the Canon 70-200mm f/2.8L IS (with stablization) costs $1700-2000. Canon and Nikon have multiple camera bodies and lenses that you can upgrade as your skill and need increase. Sony has only one camera body. And you won't know what Sony will do in the future. Sony sometimes spent a lot of money venturing into something, and when the product does not catch on as they expected, Sony abandoned the product.
If you are planning on getting just the entry level camera and the kit lens, then it really doesn't matter which one to pick. But if you think that your photographic needs may grow and expand, then Pentax is a more economical system. Nikon and Canon have higher quality and wider selections, but are also more expensive. Time will tell about the Sony system. I think you need to wait and see how the second generation Sony D-SLR turn out before you judge Sony. Hopefully Sony has kept the original Minolta's creative R & D team to design their next generation D-SLR. With more financial resources from Sony, there can be some exciting new product to come.
Olympus, Leica and Sigma are pushing out their four-third systems, but the selections of four-third systems are somewhat limited at this time.
I will recommend Canon or Nikon, but if you want a more economical system, then Pentax is a decent choice. It is a toss between Canon and Nikon. I personally use Canon and love the system. Nikon users will say the same for their system.