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42. Marissa Mayer
VP, Search Products and User Experience
Google (GOOG)
2009 rank: 44
Age: 35

It's her job to make sure Google's moneymaker -- the search engine -- stays ahead of the game. To wit: Google Instant, which delivers results as users type their queries.

NEXT: Susan Wojcicki
Last updated September 30 2010: 2:47 PM ET
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