Kings most recent book 11/22/63 entered 2012 at the top of the NY Times Bestseller List.
Lilja's Library has a good post about past number ones (nearly every book written by King) and the amount of time spent at the top of the list.
The critics have been very kind to this book, and with good reason, but it's really gratifying that in his fifth decade of publishing books, King is just as popular as ever, if not more so. The reading audience is changing, but they still love Stephen King. That's pretty amazing.