SnorgTees sells humorous t-shirts, and if you can come up with a design or a slogan they like, they'll pay you $150, plus they'll give you one free shirt from their site. Submit by email as often as you like. To get an idea of the kind of humor they're looking for, two of their current shirts are
I'm not a therapist.
Solve your own problems."
"The name Pavlov rings a bell."