The Runcam 5 is the latest HD cam suitable for FPV quadcopters released by renowned FPV camera manufacturer Runcam. It is a cube form factor following on from the shape made popular by the now discontinued GoPro Session 4 and Session 5 cameras. It measures 38mm x 38mm x 36mm which is nearly identical to the Session meaning it fits easily in to the commonly available 'GoPro' mounts. My Runcam 5 was ordered from Banggood and can be found at the link here: RunCam 5 12MP 56g Smallest 4K Cam HD Recording. It retails for $99 and can be had on special for a little as $87 - see my coupons page for up to date discount codes.
RunCam 5 12MP 56g 4K Cam HD Recording 145 Degree NTSC/PAL 16:9/4:3 Switchable FPV Action Camera Bulit-in Battery for RC Racing Drone