When Green Lantern was first published, his ring was a magic item created from a meteor. Later it was retconned to be one of the normal rings. The New 52 Alan has a ring powered by The Green, the same thing that Swamp Thing and Poison Ivy use. I'll probably go with a normal Power Ring though.

Edit: Oops, got ninja'd. It was weak to yellow, though. The great Green Lantern, taken down by a banana xD