all cameras you have listed are good. Perhaps you would like to do a search for comparison between the Sony A300 & A350.
I would also urge you to go to a store to try out the cams you have shortlisted to see which is more comfy to you. As you are the one using the cam, you have to feel it for yourself to see which is more comfortable. Do play around with the camera settings to see if you're comfortable with the interface. Lastly, to test the image quality, you may want to make sure the settings of the camera are the same and do not be affected by the sales person cos they will always recommend something which yiekld them the most profit/commission. Listen to your heart.
Buy into the system, not into the body alone. Also think about how wide the range of accessories and lenses are, the availability of the products in stores, the 3rd party accessories available for it and how committed the brand is to the market. Indeed, buying your first DSLR is not a easy step at all. It is a commitment to a brand for better or worst. "Divorce" is of course possible but expensive so choose your camera system properly and not on a whim.
Never never never buy a camera body + lens no matter how good the bargain if there is little availability of accessories and lenses because when the time comes when you want to step up from what you have, you find that you don't have much choice at all.
Well, everyone have their own preference on which camera should one get. Most importantly is how comfortable are u holding the camera and functions. Before i got my 450D, i tried nikon models too. *bleah* Hope it helps.