The 1972 Flintstones Colorforms set:

I had it. I got a set in Christmas of that year (I only know it was '72 because that's what the ebay listing said). Colorforms were great on a rainy day, because basically those were the only days I could use it. Unless it was raining, I had to be outside. I can still remember the taste of the pieces, because they eventually all ended up in my mouth...