Aw, I love Popeye! My favorite cartoon that came out in the 50s is Rocky and Bullwinkle (1959, but that still counts) . It had a lot of really fun segments, like Fractured FairyTales, Dudley Do-right, and Mr. Peabody and Sherman (the original is actually good I promise)
The best part was Boris and Natasha. Yes, they were huge Russian spy stereotypes and a product of the fears of the Cold War, and we should acknowledge that, but they also had great chemistry from each other, they loved being bad and went back and forth being each other's straight man.
I personally have a great love of sixties cartoons, Super Chicken being a favorite. Watch it for Fred alone.