I am surveying small, locally streaming cameras for applications in art installations. The focus is on affordable, hackable, wearable cameras for performance or interaction applications.
Recently I tested the Nextech mini wifi camera - a handy device for portable realtime video streaming where latency is not a major factor. Battery powered, good IR illumination at night, small and light.
This is a good example of a Raspberry pi approach that focusses on low latency - particularly helpful when using for tracking gestures, sonifying, or video piloting. The system above uses UV4L that allows you to capture and stream an HDMI output. So you could, for example, build an openframeworks app displaying a fullscreen video feed and then forward the fullscreen output of that application as a low latency MJPG stream.
Another pi-based approach would be to send video via NDI with Dicaffeinate. NDI is very easy to receive in frameworks and video tools - TouchDesigner, OpenFrameworks etc. making a simple set up. Latency and quality are hardware dependant and an rPi might not be up to the job if latency is primary concern