I just bought a 3/4 for the same reason. I wanted to be cooler on hot days but still have good protection. I got an HJC IS-33 II. It has a ratcheting face shield that I leave up at slower speeds. It also has a drop down sun shield which is really handy in changing light conditions. It's also a must if you have glasses with photochromic lenses. Those lenses won't darken with the shield down because the plastic blocks the UV that triggers the process.

They're not easy to find, but the Shark Evoline modular helmets let you fold the chin bar all the way back, essentially converting to a 3/4 helmet with removing any parts. I've never seen another one like it.