Gatherings of a retired teacher . . .

David Pleacher is a retired mathematics teacher who has maintained a math page on the Internet since 1998 -- and one of his rich and varied collections of resources includes mathy poems and songs, some by him and some by other authors.  Here are two samples:

by David Pleacher, found here

Two ways to compute 1/3

Here, from Betsy Devine and Joel E Cohen, is a "mathematical" limerick:  
     

An Integral Limerick