What ... me worry about “scammy” ad accusations? Social gamer Zynga may be struggling with an image problem stemming from its offer-based in-game ads, but an SEC filing shows that the company just got a fresh influx of cash—$15.1 million in a third round of funding—so clearly, its investors don’t seem to be worried about the recent fallout.

Zynga has raised over $54 million in total, including a $29 million round last July. Previous backers include KPC&B, Union Square Ventures, Institutional Venture Partners, Foundry Group and Avalon Ventures; private investors like Reid Hoffman and Bob Pittman also participated in Zynga’s first round. From the filing, it looks like KPC&B, Foundry Group and Hoffman re-upped their investments for this round; it also lists new hires and Yahoo alums Vish Makhijani and Reggie Davis as board members. We’ve pinged Zynga for confirmation.

EA’s Playfish acquisition leaves just Zynga and Playdom as the two big indie social gaming companies, and now both have built up their war chests—Playdom raised a $43 million first round last week—for acquisitions and new game development in 2010. Various reports have insisted that Zynga is eying an IPO late next year, though, with the company’s recent (temporary?) shift away from the offer-based ads, it may need to show potential shareholders that it has a more sustainable, less “scammy” source of revenue, before they’ll buy in.

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