David Lawee may think Android is Google's best acquisition, but from a pure ROI perspective it's hard to beat Applied Semantics, which built AdSense -- the paid search advertising platform that's still responsible for most of Google's revenue and profits.
#9 (tie): dMarc automated radio ad placement, $102 million
This one was a mistake: in 2006, Google paid $102 million for this platform for automatic placement of radio ads, and offered a whopping guarantee of up to $1.1 billion based on performance. But the business never took off, and Google shut the program down in mid-2009.
