Ball? How on God's green earth did the ball not make it in as the FIRST ENTRY INTO THE HALL OF FAME.
The ball has been a play thing for LITERALLY ALL OF RECORDED HISTORY. If there were ever a more iconic item in the world of toys it is the ball. Seriously, as Buzznut said, there are so many different balls in use right now, not to mention rubber bouncing balls, hamster balls, and jinglying balls-on-a-stick-that-look-like-distance-counters (you know what I'm talking about all of you with who had 1-year-old's in the 80's). And that doesn't even scratch the surface of the ubiquity of the "ball" toys.
The ball...seriously...