I had a moment myself where I managed to do a 180 and return in a 172, although the engine was still producing some power and that was enough!
I did see an FAA/AOPA DVD on this subject. They calculated that from about 700ft (can't remember the exact height) it was possible to make a 180 and land. The key was using the appropriate bank angle which was between 45 and 60 degrees. This was based on calculations that a steep turn would have used up less altitude than a shallower turn by the time the 180 was complete. Was a bit of an eye opener.