I was going to hijack a footie thread with this one, but decided that since I was playing air cowbell along with most of these while typing the list. It was worthy of it's own thread.
From Spin:
The Fifteen Greatest Cowbell Songs of All Time:
1) "Mississippi Queen", Mountain: The cowbell jam to end all cowbell jams. Mountain are to the cowbell what Dostoevsky is to the Russian novel.
2) "Funk #49", the James Gang: A cousin to Led Zeppelin's equally cowbell-tastic "Moby Dick"; drummer Jim Fox sauces his mid-tempo solo with some wicked 'bell, launching a thousand beer commercials.
3) "(Don't Fear) the Reaper", Blue Oyster Cult: When you're thinking about killing yourself-with cowbell!
4) "Photograph", Def Leppard: During the pensive prelude to the chorus, Joe Elliott proclaims himself a "rock'n'roll clown", but Rick Allen's cowbell answer ain't no joke.
5) "House of Jealous Lovers", the Rapture: Vito Roccoforte is Italian for "Good God, that cowbell player is totally bringing the heat!"
6) "Honky Tonk Woman", the Rolling Stones: No cowbell intro has ever sounded more like the bell around the neck of an actual cow.
7) "Saturday Night", Schoolly D: The Rosetta stone of cowbell-based hip hop, later big-upped by the Roots ("Without a Doubt") and Jay-Z ("99 Problems").
"Electioneering", Radiohead: Postmodern alienation, thy name is cowbell!
9) "Silence Kit", Pavement: Auxiliary Pavement percussionist Bob Nastanovich's finest hour.
10) "Everybody's Got Something to Hide Except Me and My Monkey", the Beatles: Ringo earns his Starr status, rattling the cowbell like he's just cooked up some chili and wants us back at the bunkhouse, like, now.
11) "Hey Ladies", the Beastie Boys: Puts the "bell" in bell-bottoms.
12) "Evil Woman", Eletric Light Orchestra: It doesn't bother me that you slept with all my friends, but you've never shown my cowbell skills the proper respect. You're evil!
13) "Calling Dr. Love", Kiss: You're wanted in the OR to administer an injection of cowbell-stat!
14) "Low Rider", War: The secret of this Long Beach funk classic? Es el cowbell, tonto!
15) "Private World", the New York Dolls: Cowbell + slap-back echo = double your cowbell pleasure!