Without knowing what your goals of the camera is (just monitor or do you want identify?), this thread is used as the go to for the new person here outlining the commonly recommended cameras (along with Amazon links) based on distance to IDENTIFY that represent the overall best value/best bang for the buck in terms of price and performance day and night. It might be a 2MP camera in some instances. Many here feel 4MP is the current sweet spot for these cameras.
And coupled with that thread is this great thread which will show why all of the same 2.8 or 3.6mm cameras is the wrong choice (these are the common focal lengths consumer brands sell):