A few big developers have dominated the social gaming headlines this past year: Zynga, Playfish and Playdom. But a range of others having been rising up on our AppData leaderboards, including RockYou, CrowdStar, 6 Waves, to name a few.

Fortunes can change quickly on Facebook’s platform. We should not necessarily assume the companies that have gotten big this past year — or in the past few months — will be dominant next year. Indeed, traffic to almost all social games has dropped in the last couple weeks in a double-whammy of users being distracted by the holidays and new policy changes from Facebook impacting how developers can communicate with users.

The next year should see lots of turbulence on the leaderboards, as talented developers from other parts of the gaming industry move in, and as the spam-laden viral channels that many leaders have relied on continue to get shut down (er, reoptimized).

But here’s an overview of where the current Facebook social gaming leaders are. Note: while some of these companies also have significant presences on MySpace, the iPhone and other gaming platforms, Facebook offers both the largest platform and the most visibility into traffic, so it is what we focus on, below.

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