David Sze (Greylock Partners)

Product guru led Greylock's investment in Facebook in early 2006 when it was still a closed network of 10 million co-eds. He has since led the firm's investments in soon-to-be-public LinkedIn (Greylock holds a 16% ownership stake), Pandora (14%) and Digg. His other investments include Revision3 (online video service), Oodle (online classifieds), VUDU (online video service acquired by Wal-Mart Stores), SoftCoin (interactive promotions outfit acquired by You Technology) and New Edge Networks (acquired by EarthLink).

Sze served as head of product strategy at Excite and worked in product marketing at Electronic Arts and Crystal Dynamics before jumping ship to Greylock. That product insight scores big points with entrepreneurs: "He is crazy smart and understands product better than anyone," says one.