Quora provides.

As of the close of 2010, what are the most recent sales numbers (or estimates) for the iPad?

Interesting discussion, but Philip Elmer-DeWitt from Fortune came through with the most accurate numbers.

"I've surveyed a couple dozen analysts, professionals and amateurs. Unit sales estimates for the quarter that ended Saturday range from 5 million to 7.54 million. Average estimate: 6.31 million. That would bring Apple's calendar 2010 iPad sales to roughly 13.8 million units."