I can't find the vid online, but Will Ferrell played the cowbell with Queens of the Stone Age when he hosted a couple seasons ago. So maybe you were thinking of both performances and got them mixed up? Either way, the QOTSA performance was hilarious. I'd look for that too.
iTunes Top Downloads -- May 06, 2012 This is a moment in time snapshot of the current top downloads from iTunes. We take a snapshot each week at the same time and post it here. To preview the songs, click on a link.