Francisco Gabilondo Soler was a fantastic Mexican writer of songs for children. He's better known as "Cri Crí, el Grillo Cantor" ("cri-crí" imitates the sound of crickets, as he is known as "the Singing Cricket".)
Here's a little song for practicing "rr" sound in Spanish:
http://www.cri-cri.net/Canciones/corochicharras.html
(Sorry, the spelling in the page is not perfect)
"Mp3" button plays the song.
Have fun!
