It looks like a no-brainer now, but when Google bought the video-sharing service in 2009, it was a huge risk: YouTube was full of copyrighted content that users uploaded without permission, and faced potentially billions in lawsuits. Google skillfully negotiated contracts with content owners and instituted a reasonable takedown policy, and as a result YouTube has thrived -- analysts estimate it's now profitable and earns more than $1 billion a year. This year, Google is increasing headcount by 30% and is hiring tons of new ad sales people.
#1: DoubleClick display ad technology, $3.1 billion
The 2007 acquisition of DoubleClick launched Google into the display advertising business. It's been a mixed bag. Google boasts that it's making $2.5 billion a year from display, but about $1 billion of that is from YouTube. Also, display advertising isn't nearly as profitable for Google as its core search advertising business. Still, display advertising is a big business, and Google has to be in it. Buying DoubleClick was a lot faster and easier than building a display business from scratch.
Now, check out what Google will get from its biggest acquisition ever: