The official dashboard is http://developer.android.com/about/dashboards/index.html and has been updated fairly often - maybe once a month or so - since ICS released.

According to that chart, about 84% of devices that have accessed Google Play are on Froyo or Gingerbread, and another 7% are on ICS.

Pretty much all of the phone market is concentrated in Gingerbread and Froyo. I think fewer than 10 types of phone are on ICS.