When I created my Mad Lib Valentine illustration (in my Illustration gallery) I offered a free sketch to whomever filled in the blank speech bubbles with the dialogue I liked the most.  The girl who won is a fan of my Godlings comic, and requested a sketch of herself as a Celt and her boyfriend as an Aztec.  I enjoyed working on this so much, that it developed into more than a simple sketch, and worthy of joining my Character Design gallery here.