The data journalism handbook is a free, open source reference book for anyone interested in the emerging field of data journalism.
It was born at a 48 hour workshop at MozFest 2011 in London. It subsequently spilled over into an international, collaborative effort involving dozens of data journalism's leading advocates and best practitioners - including from the Australian Broadcasting Corporation, the BBC, the Chicago Tribune, Deutsche Welle, the Guardian, the Financial Times, Helsingin Sanomat, La Nacion, the New York Times, ProPublica, the Washington Post, the Texas Tribune, Verdens Gang, Wales Online, Zeit Online and many others.
You can buy the book or use the free web version online.
That's not all, here's a list of great high quality content free online UX books I have personally picked and recommend you to go through: Free User Experience books (Interaction design, HCI, web accessibility & Information Architecture)