Q: Why don't they play poker in the jungle? A: Too many cheetahs

Q: Why do hummingbirds hum? A: Because they don't know the words.

This discussion was created a while back, and has plenty of good jokes: http://www.italki.com/discussion/75734

"I used to be an adventurer like you, but then I took an arrow to the knee." Sorry, overused and pop culture heavy, I just couldn't resist.

Avoid jokes. They are risky even for native speakers. The risks are: most of the so-called jokes are not funny; even more are juvenile or bad taste or both. Humour is another matter. Most of the time humour has nothing to do with jokes.