Android (2005) – The Android name might be well-known now, but in 2005 it was a 22-month-old startup that nobody knew anything about. Part of that was intentional, as co-founder Andy Rubin kept a tight lid on the company's mission. Today, it's the core of Google's mobile operating system, powering over 300 million smart phones and tablets. Not bad for a deal that was estimated to cost Google just $50 million.
Applied Semantics (2003) – While the purchase of this then- 45-person large business didn't sound sexy at the time (face it, whose socks are knocked off by a company known for its semantic text processing technology?), it's arguably the best purchase Google ever made. The $102 million price tag might have seemed steep at the time, but it proved to be a drop in the bucket once the Applied Semantics team built AdSense — the paid search advertising platform that today makes up the majority of Google's revenues.
"Next step in the evolution of the Internet"
YouTube (2006) – The $1.65 billion dollar purchase of YouTube in 2006 caught the world's eye, but the company employed just 67 people at the time. YouTube was an up and coming star in those days, but a lot of critics had questioned its staying power, noting looming copyright infringement suits. Then-CEO Eric Schmidt was so bullish on the company that he called it "the next step in the evolution of the Internet" — and fought off competing bids from Microsoft, Yahoo and News Corp. to lure the company into the fold.

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Youtube
Zagat (2011) – After a long string of tech acquisitions, Google threw everyone a curve in September 2011, announcing plans to acquire this popular review service. The $151 million purchase (which followed a failed attempt to buy Yelp) was meant to help shore up Google's burgeoning local service, adding another tool for people to find quality local offerings quickly. Tim and Nina Zagat, who founded the business more than 30 years prior, stayed with the company, as well as an unknown number of its 40 in-house editors.
Where2 (2004) – In 2003, Danish brothers Lars and Jens Rasmussen founded a small mapping technology company, but had grander plans to revolutionize how people got directions. When Google heard those plans – and saw the prototype the Rasmussens and two associates had created – it quickly bought the company. The result was Google Maps, which has gone on to become one of the company's most popular features. It's a primary navigation tool for Android phone users and has been a key part of the iPhone to date, though Apple will replace it with its own map technology later this year.
Picasa (2004) – In the days leading up to its IPO, Google bought this online photo manager in an effort to maintain its lead over Yahoo and MSN, which were still viable competitors to its primary search business. Picasa was a project from the Idealab business incubation studios (whose other success stories include NetZero, search tool Overture and PetSmart.com) with fewer than 30 employees at the time. It grew to be a favorite tool of Web-based photobugs and a worthy competitor to Flickr (which was acquired by Yahoo).
The ink's still wet on this deal. What's next?
Apture (2011) – Contextual searching — searching for further information without having to leave a Web page — is a growing field and one that Apture helped kickstart. Google was impressed with what the then four-year-old startup (which had raised $4.6 million in funding) put together and last year brought both the technology and the staff over to its Chrome browser team to help enhance the product.
Meebo (2012) – Since its founding in 2005, Meebo has explored several different corners of the online social space, but it's best known for its Web-based instant message service. Along the way, it built up a staff of 200 people, collecting more than $60 million in funding total. The ink's still wet on the paperwork following the Google purchase, but expect Meebo technology to wind up being incorporated into Google+ in the months to come.
Sparrow (2012) – Gmail might be a tremendously popular hub for people's email, but accessing it on your iPhone can be a pain. Apple's mail interface regularly hits snags and Google's own app was disappointing. So when Sparrow hit the iPhone, it quickly gathered a following. Users could view up to 1,000 messages offline and it supported priority inboxes and labeling. Google hasn't said what it plans to do with the app yet, but supporters are hoping the company will use it as a framework for its next iOS efforts — ensuring Gmail is a cross-platform success.

Pyra Labs (2003) – While Pyra Labs may not be a familiar name, its Blogger service was a big part of the reason Weblogs exploded onto the Web. Launched in 1999, it almost shut down in late 2000 as the dot-com bubble burst — but rode out the storm by operating out of the home of co-founder Evan Williams. As the online economy began to pick up, Pyra Labs operated with a skeleton staff of six people, but its easy to use tools gave everyone who had the urge to create an outlet for their thoughts the opportunity. Once Google bought the company, Blogger saw its user base grow into the millions.