Within the subset of certified, normal category piston aircraft, you will find one of these two on a sizable proportion of those airplanes.

[1] https://en.wikipedia.org/wiki/Lycoming_O-360

[2] https://en.wikipedia.org/wiki/Continental_IO-550

To my knowledge some ultralights use regular unleaded (called MOGAS in some aviation contexts) and of course anything that you can buy an airline ticket for outside of perhaps Alaska will use jet fuel.