Wow!! That's amazing--your story sounds just like mine.
My son had normal speech patterns until he stopped babbling (and was just listless) after his 4 month vaccinations. He continued to be a quiet child afterwards.
We did buy Baby Babble--it's cute, but it never made my son babble. It's poor quality and doesn't really teach anything (maybe 3 signs total). But it's worth a try, I suppose.
We also did 1 year of speech therapy through Early Childhood Intervention--it's FREE if you're in the US and your son is at least 3 months behind in some skill.
Now, he's 2.5 years and he can sing full songs, count to 20, tell us stories...so don't worry!!