Lets laugh

From Monty Python:
Q: What's brown and sounds like a bell?
A: Dung!

Honorable Mention, an original work by my younger brother:

Q: What's also brown and sounds like sonar?
A: (In a high voice) Poop!

From Bloom County:
Q: Have you heard about the new corderoy pillows?
A: They're making headlines!

Anonymous:
Q: Why did the monkey fall out of the tree?
A: Because it was dead!

Honorable Mention:

Q: How did the dead monkey cross the road?
A: It was stapled to the chicken!

From a friend:
1: Ask me if I'm a tree.
2: Huh?
1: Ask me if I'm a tree!
2: Uh...are you a tree?
1: No!!!
(End of joke.)

For the kindergarten crowd:
1: What did the apple say to the banana?
2: I don't know, what?
1: Nothing idiot, apples can't talk!
(Repeat with various objects at least 37 times, or until shot.)

The strings-go-in-a-bar joke, repeated here for those who haven't heard it because they were just thawed out of glacial ice:
These two strings go into a bar, and ask for a drink. The bartender says, "Hey, I don't serve your kind here, you're just a couple of strings!" One of the strings ties his ends together and says, "Frayed knot!" Get it? Frayed knot? Oh wait, maybe that's not how it goes, it's...hey, wait! Come back!

Absolutely any joke involving a dog named Sex.
Another winner from my brother:
1: Knock-knock.
2: Who's there?
1: Knock-knock.
2: Who's *there*?
1: Knock-knock.
2: Who's THERE!?!
1: Knock-knock.
2: QUIT it, dammit.
1: Knock-knock.
(Great for starting fights.)

The good old "any key" joke, usually reprinted by the microcephalic when they discover desktop publishing and feel compelled to include "humor" in a "newsletter":
1: I can't use my computer!
2: Why not?
1: It says "press any key".
2: So what's wrong?
1: I can't find the "any" key!

Anonymous:
Q: How do you keep a moron in suspense?