The Awl has collected from "43 music writers, editors, critics and assorted Awl music lovers... the most played songs in their digital-music libraries, as counted on iTunes or Spotify accounts." For example:

Amanda Dobbins, New York Magazine
“Rolling in the Deep” by Adele, 1748 plays

Caryn Ganz, Spin
"’Till the World Ends" by Britney Spears, 58 plays

Sasha Frere-Jones, The New Yorker
“Katy On A Mission” by Katy B/“Tangerine” by Led Zeppelin, play count n/a

That "n/a" is a cop out, SFJ! And sorry to hear about your breakup, Amanda (there can be no other reason to listen to a single Adele song 1,748 times, right?).

I wish I had one to share, but I don't have my home computer here to check. I only remember one time years ago, when a coworker borrowed my computer and discovered while browsing my iTunes that Kelis's "Milkshake" was my most played song. I didn't even know the thing was keeping track. Dang you, technology!