My son's first word was "Mama" followed by "DaDa". He also says, "Yay!" (while clapping his hands), and "Boo" (when we play peakaboo with him)
He says "Baba" and "Hi" and he sometimes even sings "lalala"(that's usually in the car with the radio).
And...13-18 months? Mine just turned 10 months! I think he says quite a lot. He is at that stage where he attempts to copy everything we say and we work with him as lot when it comes to words.
He says the words "Dada" and "Yay!" the most.
I thought it was interesting that "Yay!" wasn't on their first words list. It was like my son's third word. I am still trying to get him to say "bye". Currently his favorite thing to do is scream...but "AHHHH!" is not on that list either.