CineMon
Professional camera monitor for iPad. Requires a capture card.
A relative newcomer in the space of professional HDMI monitor apps for iPad and Mac. Includes a patent pending, image-based spot meter tool that can show actual scene luminance values (relative to middle gray) by placing a set of movable probes on the video feed. This seems to be the killer feature of the app, since it allows you to get accurate exposure measurements in stops and visualize contrast ratios without using a manual light meter.
This feature currently works with supported log encoded video signals from Blackmagic Design, ARRI, Sony, Fujifilm, Canon, Nikon, Panasonic, and RED.