In order to become fluent in Japanese and reach the level of a native speaker, you have to leave the textbook behind at some point. The school I went to (Naganuma) handed out copies of newspaper articles at the advanced level. Another great resource is Aozora (blue sky), a free online library similar to Project Gutenberg.
Aozora was founded in 1997 and archives books for which the copyright has expired under current Japanese law or were released by the copyright holder into public domain. Some works may disappear in the next few years if the U.S. can force Japan into “harmonizing” their copyright law and extend the length of copyright to protect the interests of big publishers. Some classic works still sell well after all. Project Gutenberg and other online archives are facing a similar threat as copyright term extensions are in discussion for other trade agreements too.
What can you find at Aozora.gr.jp? Books, and lots of them. All works have been scanned in and are published as text files. This will come in handy if you are using an electronic dictionary on your smartphone or PC. Many of the greatest writers both from Japan and foreign countries are represented with their work.
One of these writers is Natsume Soseki, a Meiji period novelist who is famous for works like I am a Cat (吾輩は猫である) and Sanshiro (三四郎). His portrait was printed on every 1000 Yen note from 1984 to 2004 before Japan introduced a new 1000 Yen banknote with bacteriologist Hideyo Noguchi on the front. Contemporary novelist Haruki Murakami calls Natsume his favorite writer.
Besides Japanese writers, non-Japanese writers are represented in the archive as well. Fancy reading Romeo & Juliet in Japanese? Aozora has this play available.
Excerpt from Romeo & Juliet.
Except for romanized names, the whole site in Japanese. You can search using the name of the author or the book, the search on the top of the page utilises search engines such as Google. Aozora also offers a more fancy looking page called 青空inBrowsers that not only has a search feature but also allows to read the text from right to left.
Most ebooks are available as a text file or HTML document. Both formats include the Furigana. Personally I prefer HTML, because Furigana are printed above the word and not in the text, making them less distracting.