Most of the ones that I wanted to put here would probably be a TOS violation, so I'm going to pass on those ones!
But here are few good ones that I like that aren't too horribly dirty:
A pirate walks into a bar with a steering wheel sticking out of his zipper.
The bartender says, “Did you know you have a steering wheel attached to your crotch?”
The pirate replies, “Arrh! It’s driving me nuts!”
***
And, because this is a frequent travel board,
here's a link to a good joke as well. 