Polish books on the Web
There is an ever-growing body of free Polish e-books on the Net. Unfortunately, due to copyright restrictions, often the works digitized are quite old.
To access full text of many Polish classic works go to Virtual Library of Polish Literature = Biblioteka Literatury Polskiej w Internecie
Another website that provides access to Polish literature and translations of foreign works is Polska Biblioteka Internetowa. [Technical Note: As of 3/23/2015 this site is experiencing issues]
Polish press
There is plenty of Polish press on the internet. Here are some links that should lead to you a wide variety of publications, from the major national publications to the local press.
For a list of Polish press in English, check out world-newspapers.com.
Digital Libraries
Poland is investing heavily in the development of digital libraries (biblioteki cyfrowe). For a virtual library which will give you access to over 600,000 works residing on the servers of Polish libraries, visit the site which allows you to search them all simultaneously: Federacja Polskich Bibliotek Cyfrowych.
Another site that gives you an overview of major Polish digital libraries is NuKat, the Union Catalog of Polish Research Libraries Collections.