Barnes & Noble Inc. joined the growing electronic reader market yesterday with its launch of the Nook. The electronic reader allows customers to use AT&T;’s 3G wireless network to buy and wirelessly download titles from BN.com’s e-bookstore that features more than 1 million e-books, newspapers and magazines.

About 500,000 of the books available at BN.com can be downloaded free through an agreement with Google Inc., which provides electronic versions of books no longer covered by copyrights that Google has scanned from university libraries. In a feature that sets it apart from Amazon.com Inc.’s Kindle and Sony Corp.’s Reader, the Nook also enables readers to lend their digital books to friends for 14 days.

We asked our customers what they wanted in an eBook reader, and specifically designed Nook to be the most full-featured, fun, stylish and easy-to-use eBook reader on the market, says William J. Lynch, Barnes & Noble.com president. He also noted that before customers buy the electronic reader they can visit the retailer’s stores to see, touch and hold Nook. That also differentiates the Barnes & Noble offering from the Kindle as Amazon does not have bricks-and-mortar stores.

The Nook has dual screens-color touch screen controls and a grayscale text display that uses the same electronic ink technology as the Kindle. The Nook, which features 2 gigabytes of memory, has an SD memory card slot enabling users to add additional storage. The Kindle also has 2 gigabytes of memory but no memory expansion slot.

Barnes & Noble, No. 41 in the Internet Retailer Top 500 Guide, priced the Nook at $259, the same price as the Kindle. Starting today, the Nook is available for pre-order on BN.com. It will also be sold in Barnes & Noble stores.

In addition to the Kindle, which commands 28% of the e-book download market, according to Publishers Weekly, the Nook faces competition from the Sony Reader, which has been on the market for three years and controls about 6% of the market. (40% of e-books are still downloaded to computers.) In addition, some consumers are becoming accustomed to digital reading on advanced mobile phones like the iPhone, making smartphones a rival to all dedicated e-book readers.

While the electronic reader market is small, it is burgeoning. E-book sales grew by 213.5% year over year in July to $16.2 million and have grown 173.9% year to date, according to the Association of American Publishers. By comparison, total book sales in July grew 2% year over year to $1.54 billion.