Wow, what memories you all are bringing back!
I wouldn't call most of these "fad" toys. For example, that LiteBrite that Baren* mentioned was something I had back in the late '60s. Also the spirograph.
Thos eand colorforms were things I just adored.
Anyone remember Little Kiddles? They were tiny dolls that came inside perfumed lockets. I adored them. For some reason, my mother got me plenty of Barbie dolls (and clothes), but wasn't happy that I preferred Little Kiddles and only gave me one, I think. She did get me a book of Little Kiddle paper dolls, which I played with until they fell apart.
Speaking of paper dolls, I also loved the Betsy McCall paper dolls that came in McCall's Magazine.
Superballs
Jacks was definitely a fad that came and went. It was hugely popular when I was in 6th & 7th grade.
Easy-Bake ovens, someone mentioned those.
Board games: Anyone remember Careers? That was my flat-out favorite. Second favorite was probably Chutzpah, a very humorous Jewish takeoff on Monopoly.
Books were also favorites with me. My mother wanted me to read, of course, but she felt like buying books was a waste of money since I could get them at the library. You couldn't get Dr. Seuss or Nancy Drew at the library in those days, though, so I had some of those.
Oh, here's a fad toy I had (as a teen): beanbag frogs.
Also stuffed snakes, for some reason. These were like 6 or 7 feet long.
I never had them, but I remember friends having those little troll dolls. They keep coming back every so many years.