• by Mark Walsh  @markfwal, December 27, 2010

How big is the Kindle? Bigger than Harry Potter. Amazon announced Monday that the latest version of its e-reading device is now the best-selling product in its history, topping unit sales of the final book in the "Harry Potter" series.

The online retailer still hasn't disclosed how many Kindles it has sold to date, other than saying "millions." A  Bloomberg report last week, citing industry sources, estimated that Amazon will sell 8 million Kindles this year -- 60% more than analysts had predicted. The company said it's maintaining strong holiday sales despite competition from the iPad and other tablet computers. "We're seeing that many of the people who are buying Kindles also own an LCD tablet. Customers report using their LCD tablets for games, movies, and Web browsing and their Kindles for reading sessions," said Amazon CEO Jeff Bezos, in a statement.

Amazon introduced the Wi-Fi-only Kindle 3 in July for $139, $50 less than the prior model and $10 less than the comparable version of Barnes & Noble's Nook e-reader. Bezos cited the Kindle's price as a key factor in its popularity. Several Barnes & Noble outlets reported selling out of the Nook over the weekend, according to Reuters.

In addition to the device itself, Amazon also said it broke a record on Christmas for the number of e-books sold for the Kindle. ("The Girl with the Dragon Tattoo") was the top-selling title.) Amazon and other retailers are benefiting from a strong holiday season, with online sales overall up 15% from a year ago to $36.4 billion, according to MasterCard Advisors' Spending Pulse. On Amazon's peak day, Nov. 29, customers ordered more than 13.7 million items worldwide, a record pace of 158 items per second. It also shipped more than 9 million products across all categories on its peak day.