Caddylak Graffix publishes greeting cards and will sometimes buy freelance submissions. They don't respond unless they plan to purchase something, so if you don't hear back within 2-3 months, you can assume your submission wasn't accepted. They accept email and snail mail submissions, and payment for ideas consists of $25, your name credited on the back of the greeting card, and 25 copies of the card.
Caddylak also produces T-shirts with funny slogans. Their guidelines for cards and T-shirts can both be found on the same page. Payment for T-shirts is $25 plus one shirt.