'Tis a silly one, but it's hilarious when it stumps people. Best used verbally:

There are thirty cows in a field, and twenty-eight chickens. How many didn't?

You're in a square room with a window in each wall. All the windows face south. Thru one of the windows you can see a bear. What colour is the bear?

What is the beginning of eternity, the end of time, the beginning of every end, and the end of every place?

E, it's a really mean one when delivered verbally

Time Flies like an Arrow

Fruit Flies like Banana

But there is not like an Answer to find in that

What usually has 4 letters, sometimes 9 letters, but never 5 letters.

!It's not a question, it's a statement: "what"=4, "sometimes"=9, "never"=5!<

There is a riddles sublemmy, just fyi!

An ancient device for looking through walls?

Window.

What can run but never walks,

Has a mouth but never talks,

Has a bed but never sleeps,

Has a head but never weeps?

It doesn't lead to a destination, and maybe isn't even a riddle, but a sentence I like is:

Is your answer to this question the same as if I had asked you to give me a dollar?

When is a door not a door?

!when it's ajar!<

I fly without wings, I cry without eyes, whenever I go, darkness flies.

Edit: Another one: The more you take the more you leave behind.

What runs faster uphill than down?

(Fire)

How easy should it be to solve?

My favorite longer puzzle is “there’s a naked man lying dead in a field with a stick in his hand. Asking me only yes/no questions, tell me why he is in the field and how did he die?”

Okay, so if I build a bridge from X to Y, it's a great bridge.

If I build a bridge from A to B it's a terrible bridge.

Do you want to build a bridge?

(If the person says Okay as a part of their bridge proposal, it is good. If not, then the bridge is bad)

This is a great way to make everyone at a gathering hate you.

This one is kinda hard to describe, so I'm including an image. Four people are standing in a row and all are looking to the right (EDIT: On the image, the fourthperson is looking left. That doesn't matter, because nobody can see through the wall). First and third person have blue hat, second and fourth have red hat. There's a wall between third and fourth person. Nobody knows what color is their hat. Everybody can only see hats of people on their right side (left/right sides are from the perspective of us, seeing them from the side). Nobody can see through the wall. For example first person can see the second and the third person. The second can only see the third person. They know that two of them have red hat and two of them have blue hat. They are told that if anybody says aloud the color of their hat, they are free to go. (They are captives or something). If anybody says the wrong color, they are all gonna be killed. They can't obviously turn around, talk to each other or something like that. They can't guess. Are any of them going to tell his hat's color?

Seeing the Proposition from RagnarokOnline@reddthat.com I've got a similar one I know in French that can be translated:

I am a king, taking presents from strangers to get into my kingdom. Propose me Gifts and I will tell you if you can enter my Kingdom

You are in a room with two doors. Each door has one guard. One door leads to heaven and the other leads to hell. You have to choose one door and once you choose it, you have to go there. Before you choose, you can ask one of the guards one question. One of them always lie and the other always tell the truth. You don't know which guard is the liar/truth teller and you don't know which door leads to hell/heaven. What's the question you ask the guard?

-I cannot allow you before Théoden-King so armed, Gandalf Greyhame. By order of Gríma Wormtongue. Your staff.

-Hmm? Oh. You would not part an old man from his walking stick?

-It is not by my choosing. Your staff I judge to be five feet, yet no object greater than four feet in length may be brought before the King.

-Then I must speak with the town carpenter.

Later that day, Gandalf brings his staff to the meeting with Théoden. He has not broken any rules, and the staff is unaltered. How did he manage it?