The Hollywood Reporter, via the Wall Street Journal, reports that social gaming firm Zynga is set to file an initial public offering as early as today. The creator of FARMVILLE looks to earn $2 billion. The company believes its valuation is between $15 and $20 billion. In comparison, the WSJ pointed out that Yahoo! is valued at $19.5 billion, Activision Blizzard $13.3 billion and Electronic Arts $7.5 billion.