Here's a quick way to whittle them down: take papers from the bottom of the pile instead of the top. Why does this help? Because the oldest papers in the pile usually have the least hold on you. They're either out of date, no longer applicable or ready for filing.
Generally you can tell which category they're in right away and make a decision on them right away too. And then, voila, your pile is that much shorter.
Pile from striatic's photostream.