The Ring Nebula, Messier 57, is located in the constellation of Lyra and is, indeed ring-shaped. It was formed from gas ejected by a dying star barely visible at the centre of the ring.
This deep space object was quite faint, and we find it remarkable that Antoine Darquier de Pellepoix and Charles Messier could actually see this with telescopes in 1779.
http://en.wikipedia.org/wiki/Ring_Nebula
Ouareau Forest Deep Space Observatory 