The University of Pennsylvania has put together a nice webpage with links to over 25, 000 online books that is certainly worth a look. A quick perusal of the items on offer raises the question: why are some books available online while others are not? Many of the books you’ll find online in full text are old enough that they fall in the public domain. While copyright laws are extensive, they do have limits in terms of longevity. For a roundup of copyright law and the public domain take a look at this webpage from Cornell University.
So while it is possible to read Huckleberry Finn online from sources like Project Gutenberg, your most likely not going to be able to find your recent text book for free online. However, the Regis Libraries do offer access to several electronic book collections including Books 24X7 and NetLibrary, which provide you access to copyrighted materials licensed for use by Regis University students. All of these sources are worth investigating!