Price: $750 million
Announced: November 2009
FTC Approval: May 2010
The purchase of AdMob is consistent with the strategy already exhibited by this list: Google aggressively ramping up its advertising inventory. Along with Invite Media and AdMeld, this plunged Google into mobile advertising. Mobile apps are an increasingly important venue for ads -- just ask anyone who plays Hanging With Friends.
Google announced in May that in its first full year with the company, AdMob grew by over 3.5 times, getting over 2.7 billion daily ad requests. The company plans to use the AdMob network in further integration with DoubleClick's ad tools to ultimately operate on a single platform across all devices.
NEXT: 3. YouTube