So I'm reading Slashdot the other day and I find an entry pretty deep in the board where someone mentions that in their sig(nature) (for their Slashdot user account) that they have a link to their website of free books.
I don't log in to Slashdot so I don't have anything set up for my account, thus I don't normally view sigs. Intrigued, I go to this user's posts and look up their history to get the address of this website that may or may not be worth it. Why am I doing this? I'm uncertain, but I really, really like to read. Maybe that's it?
Anyway, I find The Assayer. Click on Browse by Subject to see what he has collected. I've skimmed it very briefly, but it looks like it has quite a bit of books. I'll check out the Math/Programming sections sometime this week/end, hopefully.
If Science Fiction and/or Fantasy is more your bag, baby, please check out Baen Books. Downloadable books in a variety of formats. I've read only about five or six from Baen, but I've liked the ones I've gotten.