The dude at xkcd has setup a site to let people submit and vote on limericks.
Looking through the random submissions I found my favourite pair:
A bitter limerick connoisseur
Distressfully said “I concur
there’s no start more rank
than ‘There once was a blank’.
That’s something that we must deter.
With a suitable follow up of:
There once was a [person] from [place]
Whose [body part] was [special case].
When [event] would occur,
It would cause [him or her]
To violate [law of time/space].
Nothing like meta comentary in the form of the subject :)