Marc Andreessen

Co-founder and CTO of Ning

What you may not know: Starred in a 1999 Miller Lite commercial with Norm MacDonald that featured bad puns like "dot come here often?" Says commercial was pulled the next week and is nearly impossible to find today.

What you need to know: Besides working with Ning, which helps users build their own social networks, Andreessen is a behind-the-scenes force for a lot of open-source and Web 2.0 companies. He has mentored, advised, or funded everyone from Josh Schacter of del.icio.us, Jay Adelson of Digg and Revision3, and Evan Williams of Twitter. But don't call him; if you have a great idea, he'll find you.

Ning's estimated value: $560 million