????As Goldman Sachs, Accel Partners, and others clamor for a larger piece of Facebook and its valuation spirals upwards, here's a look back through all the VC rounds and players that fueled Facebook to be what it is today.

????When Goldman Sachs (GS) and Digital Sky Technologies invested $500 million in Facebook, propelling its valuation to a new high of $50 billion, they renewed chatter about whether the social network was gearing up for an IPO.

????Whether or not that happens remains a big question, one without a definitive answer yet. Mark Zuckerberg has said he's in no rush to take his company public, and our own Dan Primack reported that Facebook's latest round is being conducted at least in part to stop mid-level and junior employees from selling shares on secondary exchanges like SecondMarket and to keep the number of investors below the 500-shareholder threshold that would force the social network to go the IPO route. The Wall Street Journal argues otherwise, citing a 100-page deal memo from Goldman Sachs that indicates Facebook intends to pass that key shareholder threshold, positioning it to either disclose financial results or go public by April 2012.

????Whatever happens, Facebook is a lot like every other Silicon Valley startup in one key way: whether making profits or losing money, Mark Zuckerberg has taken millions in venture capital funding to give his company the best possible financial footing for success. Even as a behemoth that many speculate could be booking a billion in annual revenues, Zuckerberg still clearly felt the need for more funds by agreeing to the Goldman deal. That's because if Zuckerberg wants Facebook to be the social fabric for the web, he'll need that cash to expand, not just domestically, but in areas like Russia and China, make new tech acquisitions, and position Facebook well for mobile computing. The more cash on hand, the fewer tough choices (like choosing between cashing out some early employees and, say, building a new Moscow office) Facebook will have to make.

????Over the last six years, Facebook investors have contributed extravagant sums during multiple rounds of funding as the social network's own user base has grown by leaps and bounds. Fortune compiled a timeline tracing the investments that contributed to Facebook's reportedly $2 billion in cash reserves:

February 2004

????Mark Zuckerberg, Dustin Moskovitz, Chris Hughes and Eduardo Saverin launch The Facebook from their Harvard dorm room.

June-July 2004

????The fledgling social network receives $500,000 from Peter Thiel, president of Clarium Capital. Then current social champ Friendster is rumored to make a $10 million bid for the company, but Zuckerberg rejects it.

December 2004

????Almost one million users at Harvard, Stanford, Columbia, and Yale.

May 2005

????Thiel and Accel Partners invest $12.7 million, giving Facebook an $87.5 million valuation. Number of active users: 5.5 million.

September 2005

????The Facebook shortens its name to simply "Facebook."

March 2006

????Facebook reportedly shops itself around to buyers for $2 billion.

April 2006

????Investors including Accel, Thiel, Greylock Partners and Meritech raise $27.5 million. Current valuation: $500 million.

Sept. 2006

????Yahoo (YHOO) supposedly makes a $1 billion bid -- Facebook rejects that, too.

Dec. 2006

????Thiel says Facebook is worth $8 billion. The social network now has 12 million-plus users.

April 2007

????20 million active users.

October 2007

????Microsoft (MSFT) invests an unheard of $240 million, giving it a 1.6% stake and Facebook a valuation of $15 billion.

????There are now more than 50 million active users.

November 2007

????Hong Kong businessman Li Ka-Shing, whose companies make him one of the largest operators of container terminals, invests $60 million.

January 2008

????European Founders Fund invests $15 million.

March 2008

????Ka-Shing invests another $60 million, effectively doubling his stake to $120 million. Money from Microsoft, Ka-Shing's second investment, and European Founders Fund bring brings the total amount raised from this round to $315 million.

May 2008

????TriplePoint Capital reportedly loans Facebook $100 million.

Aug. 2008

????Early employees sell stock options. Over 100 million people now regularly log-in.

January 2009

????Over 150 million active users.

February 2009

????Over 175 million active users.

April 2009

????Facebook reportedly rejects funding at $2 billion and $4 billion valuations. Over 200 million active users.

May 2009

????Digital Sky Technologies (DST) invests $200 million with a valuation of $10 billion.

June 2009

????DST buys back up to $100 million of Facebook employee shares.

September 2009

????Over 300 million active users.

November 2009

????Elevation Partners invests $90 million. Annual revenues of $775 million and profit of $200 million.

December 2009

????Over 350 million active users.

February 2010

????Over 400 million active users.

June 2010

????Elevation Partners invests another $120 million, bringing its total investment to $210 million.

July 2010

????Over 500 million active users.

November 2010

????Accel Partners sells an unspecified number of Facebook shares.

December 2010

????Reports indicate Facebook's annual revenues of up to $2 billion and profit of roughly $500 million.

Jan 2011

????Goldman Sachs invests $450 million and DST invests $50 million, putting Facebook's valuation at $50 billion, a new high. (Goldman plans to raise up to $1.5 billion more to sink into Facebook, from its high-net-worth clients.) Moskowitz reportedly sells a substantial number of shares on the secondary market. The social network now reports more than 600 million active users.

Cumulative funds raised, excluding loans: $1.3 billion. With Facebook sitting on $2 billion in the bank after raising $1.3 billion, the total return on investment, if crudely calculated for today alone, would be 53.8%. Of course, large, later rounds of funding have allowed early investors and employees to cash out at ROIs far greater than 53.8%. The number is only worth noting since Facebook is often mentioned in tech circles in the same breath as Google (GOOG), which has a whopping $34 billion in cash reserves right now.

????Facebook, in other words, will have to grow its business several times over, and perhaps become an even larger company (it has roughly 2,000 employees now, to Google's nearly 20,000) to book that kind of income. Goldman Sachs and its investors are hoping, then, that they're right in thinking a $50 billion valuation and two-year lock-in for Facebook shares will, in 2013, look like the bargain DST got with its investment at a $10 billion valuation in 2009.