Here are some links you might find useful:

Giggle Poetry is a website from Meadowbrook Press who also publish books of funny poems.

Kenn Nesbitt is a US children's poet who specialises in funny rhyming poetry.

Fern's Poetry Club is part of the Public Broadcasting System's website.

This site on Poetry Zone is the text of a how-to book by Roger Stevens.

This part of the Scholastic site features writing with Jack Prelutsky and other well-known children's poets.