Last October, Google M&A chief David Lawee called the 2005 acquisition of Android -- the mobile phone platform started by ex-Danger leader Andy Rubin -- its "best deal ever." Less than three years after launch, it has become the most popular smartphone platform in the world.
#15: Aardvark social search, $50 million
Google paid about $50 million for social search Q&A service Aardvark in February 2010, but hasn't really done much with it yet. However, there are hints in Google+ code that suggest that Aardvark -- or what's left of it -- will soon be integrated into Google's new social network.