We all know about the mitzvah of Pidyon HaBen -- redeeming of the first born. Many of us are lucky enough to be able to perform this mitzvah.
Somewhat less well known is the mitzvah of Pidyon Pehter Chamor -- redeeming a first born donkey. In short, when a Jew owns a donkey that is the first born of it's mother, it must be redeemed from a Kohen in exchange for a sheep. This mitzvah is not done very often, as there are a number of conditions that the donkey must meet before the mitzvah applies.
Adderabbi has some pictures and video from such an event last year. I found it very interesting how they decorated the donkey and sheep for the occassion.