New York's Museum of Mathematics celebrated National Limerick Day on May 12 with an online program of contributors reading their mathy limerick stanzas. I did not learn of the reading in time to apply for participation but here is a sample I might have submitted.
In baseball the diamonds are square--
And the ball has the shape of a sphere.
Nine guys make a team--
So, two teams make eighteen--
And fans cheer when plays come in pairs.
The limericks read at the May 12 MoMath program may be found here -- and here is a link to the results of a SEARCH in this blog for "limerick." The sample offered above was posted long ago, back in April 2010.