People ask me what Canon SLR camera they should get. Actually Each Canon model has its own market, some of the features you may only find in the professional cameras. Depends on what you are looking for and your subject. You can pick from the followings
Canon XS, XSi and T1i are consider as consume camera (low-end), usually they are around $500 - $800 price range. They are lightweight with plastic housing and basic SLR features. Don't get me wrong, they are all able to produce good images. The function they are missing are for the professional to handle extreme conditions. Such as low light, situation that is not allowed use flash or require very high shutter speed to freeze fast moving object.
Advanced Amateur Cameras
Canon 40D and 50D are considered Advanced amateur cameras which come with magnesium alloy body with advance feature which allow you to get more creative photos and able to handle some extreme lighting conditions. If you are a beginner and able to afford a $900 to $1200 camera, I would suggest you skip the low-end one.
All the 1 series are considered to be professional cameras, while the 5D Mark II is considered semi-pro. These cameras are very reliable with alloy bodies while all the 1 series come with weatherproof protection. Their auto focus system is extremely rapid and more accurate than those lower end models. These camera usually have full complement of both manual and automatic controls. However, the are big, heavy and they are all missing build in flash (If you can afford $2000+ camera, you should able to afford a external flash).
You may click on the camera images to check out the latest pricing from Amazon.