National Endowment for the Humanities
Neh: Edsit Ement: There Once Was...
Part 2 of this tutorial on limerick writing demonstrates the importance of form (meter and rhyme) in limerick poetry using the exemplary and amusing work of Edward Lear.
Emory University
Emory University: The Limerick
This site gives a good description of limerick. Features details about the rhyme scheme and the different forms of limericks. References to the bawdy nature of this verse form.
Ohio State University
Limerick Special Interest Group: Some Limerick Myths
This site gives examples of some limerick myths.