Free Computer Science E-Books
e-booksdirectory.com
e-booksdirectory.com
Although if I want to really study something beyond introductory reading I use scholar.google.com and looking at the articles published in the last decade or so as well as looking at the papers citing them too be quite effective. Although that is most effective when you are researching a narrow subject and it does sometimes require you too pay too have access too the journals, something which my university provides.
Lastly there are quite a lot of recorded univerity lectures published online that cover just about any subject you'd want to study from the comfort of your computer. I'm verry happy google has made an effort to gather them at: http://www.youtube.com/edu recently altough there's other places. For computer-science in particular I've found this blog to be highly good at gathering the interesting ones: http://freescienceonline.blogspot.com/
I realize you might already know all of this but as a student I personally am quite pleased with what the Internet provides for me especially as I like (and it enables me) to go far above and beyond what is assigned as course work, when I study something.