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.
Red Hot Chili Peppers - "Higher Ground" (Stevie Wonder) and "Search and Destroy" (Iggy and the Stooges). Oasis w/Eddie Vedder - "Daytripper" (Beatles). Pearl Jam - "Sitting on the Dock of the Bay" (Otis Redding).