Green Lantern #70 (On Sale: May 27, 1969) has a nice cover by Gil Kane.
Green Lantern stars in "A Funny Thing Happened on the Way to Earth" by John Broome, Gil Kane and Vinnie Colletta. I remember this one from when I was a kid, as it has one of the strangest solutions for killing a space monster I have ever read. The Guardians call Green Lantern to take out a gigantic creature that eats gravity. OK, I know that gravity is a force and not a thing, but hey, it eats gravity, OK? Green Lantern is attacked by the creature and eventually kills it by making it eat its own shit, or as John Broome put it, "Its own waste product." I kid you not.
But this issue is not just about shit-eating monsters, it's about a toy factory on the planet Ghyra, where the circuitry in a "Hilar-Toy" goes haywire and instead of making people laugh, it causes people to fight. Unable to fix the indestructible Hilar the makers turn it off and throw it away, but it still finds itself "active" and locates a space ship in the junkyard, which it uses to escape. With no plan of where to go, Hilar sees Green Lantern fly by, returning from giving the gravity eater a shit-eating grin, and follows him back to Earth.
After a run-in with the police for jay-walking the Hilar finds a TV studio as a hiding place. There he interrupts the filming of a TV comedy show which brings him to the attention of Hal Jordan (working his first day as a toy salesman). As Green Lantern he rushes to the studio only to find that any attack against Hilar is rerouted back at himself. Some gangsters see Hilar take out Green Lantern on TV and saying that he only wants to make people laugh. They high-tail it down to the studio and pick up Hilar by pretending to find everything he says funny.
The gangsters win over Hilar's confidence and bring him along when they go to rob a train. When Green Lantern shows up, Hilar again knocks him out cold. When he comes to, Green Lantern finds the gangsters' car and begins to take them out one at a time and then turns to face Hilar. Hilar has realized that his "friends" are evil and tries to communicate that to Green Lantern telepathically, but GL is using his ring to create an impenetrable aura around himself. Lantern uses his ring to steal Hilar's gravity and he crumbles like the toy he is.
Discovering that Hilar is just a malfunctioning toy, Green Lantern returns Hilar to Ghyra, repairs his faulty circuits and as he leaves Hilar is on stage and getting big laughs with his "A funny thing happened on the way to Earth" story.
Edited by Julius Schwartz.