Happy birthday! ¡Feliz cumpleaños! Oh crap, I forgot how to say it in Esperanto. Luckily I decided to err on the side of politeness and not play you the Dora the Explorer birthday song. I guess I'll have to e-mail you or make a blog post to wish you a happy birthday the old-fashioned way. [laughter]
It's also sage_and_sea's birthday, so happy birthday, you crazy northwesterners!
According to Omniglot, "feliĉan datrevenon", "feliĉan naskiĝtagon", and "feliĉan naskiĝfeston" are all ways to say "happy birthday" in Esperanto.