Here's a cowbell groove from the studio legend, tragically insane, Jim Gordon. It's Jump Into The Fire, from Harry Nilsson's album Nilsson Schmilsson, which for people not around in the 70's will be best known from the “last day” scene from the movie Goodfellas:
Kind of like hearing them on Bugs Bunny is my only connection to a lot 30's songs that are now jazz standards. There's no shame in it. Anyhow, the groove:
There is some layering of percussion parts going on, so it's possible he's not playing the cowbell live with the drumset track. Early on, the bell drops out during the drum fills, consistent with it being played with the drums, but later there seems to be a ride cymbal sounding (it's low in the mix, and the sound is possibly from another source) while the cowbell continues, and the bell seems to continue through the drum fills. Generally the 16th notes in the first measure are played stronger than the ones in the second measure, hence the parentheses on the latter notes. Gordon's feel is totally different than what you hear from drummers playing similar music today. He's absolutely solid, but with an edge— there's a quality that's absent from later players who are more perfectly metronomic and squared away.
Audio for the complete tune after the break: