Riddle: Why is a manhole cover round and not square? Can you guess the two reasons?
Answer: 1: It can't fall through the hole like a square one could. 2: It can easily be moved by rolling.
Riddle: What do you call a fly without wings?
Answer: A walk.  Another popular answer: A Zipper.
Riddle: I'm already old when I'm born, and become young when I die, and I’m brightest in middle age. What am I?
Answer: A star! Also acceptable: the sun.
Riddle: I leave you with a thought that fades out of sight. Product of the mind, undone by first light. Creator of hope, hell and heaven above. Made by wonder, fear, and perhaps true love. What am I?
Answer: Dreams.
Riddle: I am always hungry, I must always be fed. The finger I lick will soon turn red. What am I?
Answer: Fire.
Riddle: A certain large animal lives happily and thrives here on Earth. One day, every single one of these critters is wiped out by a mysterious disease that affects only this particular animal. There are none left anywhere on earth -- they are all gone. About a year or so later, they begin to reappear on Earth again. How can this be?
Answer: The animal is the Mule. Since all Mules are born sterile, you can only get a Mule by crossing a donkey with a horse. That is how the species is able to repopulate itself.
Riddle: What can be measured, but has no length, width, or height?
Answer: The Temperature.
Riddle: With a little detective work and deep thought, the following facts can make an accurate statement. 11 is a racehorse 12 is 12 1111 race 12112. Can you figure it out?
Answer: 11 is a racehorse 12 is one too 11 won one race 12 won one too
Riddle: I am round, I am sharp, I am small, I am big, I exist, then I don't. What am I?
Answer: The Moon. It's round when it's full, it's sharp when it's a crescent, its size can vary depending upon its phase, and it's gone when it's a new moon.
Riddle: I am the runner, The pencils the chaser. I eat up the lead, I choke on the eraser. When I am done, I become another one, To be used again. I am white And blank as well. I can be folded, Into a bell. My corners are cut perfectly, My lines are straight and blue. Me having black marks or not, Fully depends on you. What am I?
Answer: I Am Paper.