Free Programming Resources
 

Another goldmine of ebook-ready material I just stumbled across...

http://freeprogrammingresources.com

And this is an older one, but still a good one:

http://www.techbooksforfree.com/

If you make ebooks out of these, please contact the authors with your works, so they can continue to embrace further creations of the same type. Also make sure you obey any copyright or licensing restrictions on the works you convert.