I don't share the scepticism of some of the other members towards Sony and particularly Olympus. Olympus is a long-time contender in the business and with the adoption of four-thirds by other companies, I don't see them going away any time soon. They are certainly not as big a player as Nikon and Canon, but they are there and IMO they are there to stay.
Regarding IQ and all that, at normal ISO (say, up to ISO640 or so), cameras by any manufacturer give you very nice images. Also, all manufacturers have a full lens-line up for the average user. So unless you have special applications in mind, you can still safely pick all manufacturers. Olympus, for example, has pioneered some things that are more and more main stream (read: Canon and Nikon have bothered to adopt them), e. g. senor cleaning and live view. So far, they haven't come around to include in-camera image stabilization (not sure whether Pentax was first or Olympus).
High ISO IQ is another matter, there Canon and Nikon do have an edge. Interestingly enough, Canon's new 50D has worse high ISO noise than its predecessor (that's because of the increased resolution, hence smaller pixel size). But whether you actually need it is another question.
Much more important than any of the above (and here I assume that you do not need any special lenses, e. g. loupe lenses or tilt/shift lenses) is
how the body feels in your hands? Does it feel `natural'? For instance, Canons and I don't get along. We simply don't. I've owned Olympus (an E-20, my first
dslr) and Nikons and they felt natural. When I tried Pentax and Sonys/Minoltas, so did they (to a lesser degree, though). I'm sure that the quality of my photos would suffer with Canons --
not because I think Canon makes bad cameras, but because `we don't get along.' This point cannot be over-emphasized: whether you like the way a camera works and feels has a direct impact on the quality of your pictures (I'm not necessarily talking about image quality, but quality of the photo). Size may matter (too large, too small) or you would like certain features (in-body image stabilization). In some instances, you will find your camera limiting (e. g. AF accuracy, viewfinder size/quality and speed), but then you can usually upgrade
within that manufacturer.
To that degree, nobody can help you. Some people who like Canons will say `get a Canon, feels great/it's a great camera!' Ditto for various people who own cameras of other manufacturers. Try to avoid reading arguments that end in a comparison of the pro bodies when you are actually interested in an entry-level dslr.
Go and try them for yourself, all of them. Don't go to a camera store where people don't know that a Canon body cannot mount Nikon lenses (happened to me once, yes, it was the last time I was in that shop
).
