6. Postini

Price: $625 million

Announced: July 2007

FTC Approval: August 2007

    Postini was one of the first partners with Google Apps and is now a core part of that area of Google's business. According to Google's Postini site, Google Postini provides security and archiving services to over 26 million users, and is a core part of its message security and discovery capability.

    Four years since its purchase, Google decided this July to use Postini email security features in Gmail, which analysts touted as a major step in bolstering Google Apps security for enterprise. Don't be surprised to see more Postini integration into Google Apps and Gmail in the future.

5. ITA Software

Price: $700 million

Announced: July 2010

FTC Approval: April 2011

    This Cambridge, MA-based travel search company made the software for travel search sites and airlines. Google's purchase troubled some in the industry, who feared for the competitive viability of clients such as Kayak and TripAdvisor. To meet concerns during a lengthy review by the Federal Trade Commission, Google first promised to honor all ITA contracts. Shortly before approval, it went a step further and "formally committed to let ITA's customers extend their contracts into 2016," senior VP Jeff Huber wrote on Google's blog.

    Now that competition has been presumably safeguarded for the next five years, Google can launch into its plans for ITA's technology: new flight search capability. Huber's post imagined a day when a user can simply type "flights to somewhere sunny for under $500 in May" and immediately see flight times, fares, and ticket vendors within Google's search.