How to list this accomplishment on my vita?
Great work ! The way I do it is under the Publications section of my CV. The following citation is formatted in the ACM style. You can modify it for your own citation styles.

J1. Smith, J. 2013. "The best paper ever". ACM Transactions of Awesomeness, 1 (4). ACM Press, NY, USA. (most read article in March 2013)