Sorry I missed this one first time around -- actually there are different versions of Buddha's birthday, depending on which bunch of Buddhists you are (we Buddhists are really like organizing a cat parade), and the dates differ. Many communities bring together what is called the Baby Buddha celebration with other stuff, so there are all kinds of different chants. My personal favourite (good for spring, and especially good for growing things in gardens) is a woman's Korean chant which goes "Chi-jang bosal" over and over again (you can do it to "Bright Morning Stars", though there is a Korean version). This is a chant to reawaken the dormant Buddha nature (the energy of awakening in the womb of life) in all beings after winter. It is used in Baby Buddha ceremonies.

On a lighter note, there is a great album of Broadway Buddha tunes called "Dharma Moon" by a member of the Zen Buddhist Temple in Chicago.

yours, Peter T.