Free ebooks
Another good source of free ebooks is manybooks.net, particularly for more recent stuff.
You need to check your local copyright rules, though: much of the stuff on there is public domain under US law (x years since publication, copyright not renewed), but will still be under copyright under life +70 and life + 50 regimes.
If you are under one of those, I'd suggest googling the author to check.
They also have a good deal of Creative Commons work - free to read and share, as long as you're not trying to make money out of someone else's work.