Sony today announced that there are more than 1 million public domain books available through the Google Books project, as Sony continues to battle with Amazon.com and Barnes and Noble.

"We are committed to ensuring our customers have the freedom to discover and read content from the widest possible range of sources,” Sony eBook Store Director Chris Smythe said in a statement.  “We’re proud to offer access to the broadest range of eBooks today – from hot new releases, to New York Times Best Sellers, to classics and hard to find manuscripts such as those available for free from Google.”

Sony's decision seems to be a wise one, as Amazon.com, Barnes & Noble, and other providers attempt to increase book catalogs in the increasingly competitive e-book market.  Last week, Barnes & Noble, which offers more than 700,000 titles, said it offered the largest online bookstore -- about 350,000 of the total number are Google public domain works.

Amazon, with its Kindle eBook reader, offers 300,000 titles to shoppers.  Amazon hasn't publicly disclosed if it will one day include public domain titles.

Another company, Plastic Logic, plan to release an e-reader sometime in early 2010, which will compete against the Kindle, Sony e-book readers, and several other products believed to be in development.

The e-book market is a fickle one, as it's relatively closed off and purchasing books is usually tied to at least one device.  For example, Amazon's content can be read only on the Kindle and an iPhone or iPod Touch, but nothing else.  The Barnes & Noble titles, however, can be read on RIM's BlackBerry smartphones or the iPhone and iPod Touch, but cannot be read using a Sony e-book reader or the Kindle.

It's possible this closed system may drive away some interested consumers who want the freedom of reading their purchased content on any device.