Recently I have placed a new D-Link DCS-5020L camera on my mobile robot. This PTZ WiFi IP camera is quite easy to use and suitable for testing with OpenCV.
Below is a video showing the detection and tracking of face using OpenCV.
The program has been written in Python and face detection is based on pre-trained Haar cascade classifiers from OpenCV. A simple code example of how to do this for mjpeg compression is under this link. For more information on how to track the movement of any object, see this article.