It's an "old" thing, but I'm sure even those who've heard of this and seen the video can get a couple of laughs out of the more cowbell sketch as performed on the television show Saturday Night Live back in April of 2000.
With guest Christopher Walken playing the record producer telling Blue Oyster Cult he needs "more cowbells" on the song "Don't Fear The Reaper".
Read an article on the sketch and what the original BOC thinks of it here.
Then skip on over to The Cowbell Project where you can get a list ... a l-o-n-g list of songs featuring cowbell. Sadly the links to remixed tracks that supposedly get better with cowbell (Billy Idol's "Flesh For Fantasy", Sammy Hagar's "Three Lock Box" and Paul McCartney's "Uncle Albert") don't work. Neither does the link to the sketch.
But don't worry! You can view the complete cowbell sketch here.