Sony announced that it has sold 300,000 Sony Readers since the digital e-reader went on sale in 2006.

Bookseller has the scoop: “So far three million books have been downloaded from its online library, which is home to 57,000 titles. The electronics giant said it planned to grow its online library to 100,000 titles by the end of the year.”

Unfortunately, Amazon has not released figures for sales of the Kindle reader. However, TeleRead cited an unverified estimate that Amazon has sold 400,000 copies. The blog also notes that Kindle currently sells “200,000 books, blogs and other items,” dwarfing the Sony Reader’s catalog.

In addition, there is another slice in the digital book pie. As GalleyCat reported earlier this week, the iPhone reader Stanza has been downloaded by 575,000 users, and the company just added 40,000 Fictionwise titles to its catalog.

UPDATE: TeleRead links to CNN figures that might put Kindle sales below Sony Reader sales.