...there were 15 of these giants, starting in August, 1964 (featuring Superman), and other issues included Jimmy Olsen, Lois Lane, Flash, Batman, Sgt. Rock, Secret Origins of many DC heroes and Superboy...
...with the last of these giants, 80 Page Giant Magazine #15, coming out in October, 1965, and featuring the World's Finest team...Superman and Batman!
Here's a quick summary of the stories in that collection!
World's Finest Comics #74
Superman, Batman and Robin are stuck trying to find an alien who came to Earth on an experimental rocket, and stop the panic it is causing with its shape-changing ability. Batman figures out the alien is a child, so plays with it to keep it busy, while Superman figures out how to make the alien homesick...
...so that the alien will let the Metropolis Marvel take him home, ending this team-up with the Gotham Guardian!
World's Finest Comics #82
Superman, Batman and Robin enlist the help of their friend, Professor Carter Nichols, who uses hypnosis to allow the heroes to travel back in time (hey, it was a simpler time back in the 1950s), and they end up in the 17th Century France to learn the identity of the Man in the Iron Mask...
...as well as meet D'Artagnan and the Three Musketeers!
World's Finest Comics #88
Yes, Luthor and Joker stop by World's Finest Comics, starting a new legal business partnership, and this attracts the attention of Superman, Batman, Robin and Lois Lane (as these villains likely have other illegal plans). Luthor and Joker unleash super-strong robots they created called the Mechano-Men to make Superman and Batman look foolish, but the team work together and eventually defeat the scheme devised by their most fiendish foes....
World's Finest Comics #97
Professor Milo makes a machine which fortells the future, one in which Superman, Batman and Robin capture members of the Condor Gang, which comes true and leads the Condor (John Titus) and his remaining members to kidnap the Professor, and that leads to a revelation of the Professor's real identity and the capture of the rest of the gang by the World's Finest team!
World's Finest Comics #81
This story starts with the World's Finest team meeting with Ka-Thar of 5956, who came back in time with a book telling tales that the heroes accomplished. Superman says he's gotten his facts wrong, and Ka-Thar threatens to reveal the heroes secret identities if they don't follow what the book says. So, the heroes follow along so that Ka-Thar will go back to the future....
World's Finest Comics #95
Batman wakes up in the Bat Cave after passing out, to find he suddenly possesses super powers! Batman and Robin then go to deal with a fire when Superman arrives, and Superman and Batman are more interested in competing with each other than solving the problem. Robin does his best to stop the battle, but ends up on the alien planet of Xlym, where Robin learns that these aliens gave Batman powers, and made Superman and Batman hate each other! Thankfully, Robin stops the alien interference, and Batman loses his newfound powers, with the friendship between Bruce Wayne and Clark Kent renewed!
End Of An Era
the Flash and Supergirl, as well as continuing Superman and Batman team-ups with World's Finest Comics #161 of October, 1966). Check back as there will be more giant coverage to come!