There's a wonderful round that goes

WE wish you a very happy birthday
A joyous and celebrated birthday
to you dear-----------
WE wish you a long long life

I also like to call people up and sing the words "happy birthday" to the tune of the Hallelujah Chorus

Haaa-pee Birthday!
Haaa-pee Birthday!
Happy birthday! happy birthday!
Happ-eee-ee Birth DAY!

Cheers- Julia