This is "When The Saints Go Marching In". I stumbled across this when messing around playing something else, but Its a really good song to entertain people with.

e------2-3-5-----2-3-5----2-3-5-3---3-------2-2---------2-3-5-5-3--3-2-3-5-2---2--------
b----3---------3--------3---------2---5---------3-3---3----------------------3---5------
g---------------------------------------------------------------------------------------
d--------------------------------------------------------------------------------------- 

This is really easy so it shouldnt take you long. Have fun learning it!