I Want A Hippopotamus for Christmas
(the song plays once you click on the link)
And a little tidbit about the song:
Gayla Peevey [ed: the singer, who was 10 when she recorded the song] herself writes in to add: "The record was released nationally by Columbia Records and because the Oklahoma City Zoo needed a hippo at the time, the song gave them the idea of putting together a major media blitz asking kids to send in nickels and dimes to raise money to buy Gayla a hippopotamus for Christmas. Matilda, a baby hippo, was presented to me, and I donated her to the zoo. In a roundabout way the song indeed helped the zoo acquire a hippo, but the song was not recorded for that purpose."