According to the Wall Street Journal, Facebook's IPO valuation of $104 billion is the highest ever for a US company at the time of its IPO, and is the second-largest IPO behind VISA Inc.'s 2008 IPO of $19.65 billion.
Venture capital investors in Facebook include Accel Partners, Andreessen Horowitz, Elevation Partners, Founders Fund, Greylock Partners, Kleiner Perkins Caufield & Byers, Meritech Capital Partners, Millennium Technology Value Partners and Technology Crossover Ventures.
Here's a link to the Wall Street Journal story: http://online.wsj.com/article/SB10001424052702303448404577409923406193162.html?
Here's a link to my prior post on market cap v. fully-diluted equity valuation:
http://www.allenlatta.com/1/post/2012/05/market-capitalization-v-fully-diluted-equity-valuation-the-facebook-example.html