In Dwarf Fortress' Adventure mode I threw a dead buzzard at a flying vulture, damaged its wing, and it died from injuries it sustained in the fall.
In Tf2 I once headshotted a soldier descending from a rocket-jump with the Huntsman.
In Fallout 3, I threw a frag grenade at a Yao-Gui(giant mutant bear) in V.A.T.S., and that didn't kill it outright, but due to the Gui's weird relationship with physics, it flew into the air at what seemed like airliner altitude, and came back down, dying from the fall.
In World Of Tanks I managed to to kill a small tank destroyer by ramming it with my Panzer III, incurring virtually no damaged to myself in the process. I also rammed two other tanks before, killing both myself and my ramming victims, that was fun.