At birth all children are citizens of the world, learning whatever languages they are exposed to.  There has been much research proving that babies can easily learn multiple languages before their 5th birthday.  They can even speak with no accent if they are exposed to foreign language before their first birthdays.

That being said, my very favorite product for teaching my baby Spanish is the Baby's First Steps in Spanish.  I bought many CD's trying to expose my baby to great children's music in Spanish and I was very disappointed.  I could not find music that was pleasant and that we would want to listen to over and over, except for Baby's First Steps in Spanish.  I wish they had more volumes available.  The product includes a 96 page book all about foreign language and children and a wonderful CD full of music and poems in Spanish.  I have not tried the other languages but they offer Italian, French, Spanish and Chinese.