I am the Executive Director of the Center for Computer-Assisted Legal Instruction. One of our projects is eLangdell Press where we publish law school casebooks under a Creative Commons license. We have a couple of dozen books so far. They are free and available as PDF, .mobi, .epub, .doc and can be purchased from LuLu.com at cost. Most of them are also available on Amazon for 99 cents.
We pay law faculty to write new books every year and are experimenting with folks writing single chapters and books with more multimedia features. You can see our work at elangdell.cali.org.
Christopher Columbus Langdell was the inventor of the casebook.