Google bought YouTube for $1.65 billion in October, 2006. Lots of money for an idea that basically was started by two guys in a garage.
Google first tried to get Google Videos going, but after that failed to catch on, they just bought YouTube instead. I doubt it will be the last website they purchase for that kind of money.
Also check out the list of Google Acquired companies... http://en.wikipedia.org/wiki/List_of_Google_acquisitions