You can get this free application from Booshaka and when you install it, a custom tab called Top Fans is added to your page.
You can view the stats of each fan listed to see how they have participated. The app gives a complete history of the fan’s activity on your page.
To install the app, just go to Booshaka and click the blue Install button. They also have a Top Fans Pro version that rewards the top fans with perks.