The debut of the Royal Flush Gang!
The Story: "The Card Crimes of the Royal Flush Gang!" by Gardner Fox, Mike Sekowsky, and Bernard Sachs. The JLA fights a team of bad guys, the stellar-powered Royal Flush Gang.
The RFG uses their powers to affect the JLAers moods, so that they become despondent over their losses and start to give up. Luckily Snapper Carr is there to give them a pep talk, and he helps them defeat the Royal Flush Gang. Wonder Woman makes him a jester's costume so he can go with them to fight the RFG, making him more of a horse's ass than he was already.
Roll Call: Superman, Batman, Wonder Woman, Flash, Hawkman
Notable Moments: Hawkgirl guest stars again, Snapper gets a large role, and the Royal Flush Gang debuts. A pretty big issue.
...but all that pales in comparison to the really big deal with this issue--the debut of DC's Go-Go checks! Yeah, dig it, baby! It's a happening!
Also, we get for the first time a new JLA logo, which I admit is pretty spiffy. The old one is almost mythic in its iconic-ness, so I'm glad they went back to it, but I thought this one was pretty cool, too.