There are a bunch of (DRM-free, multi-format) sf/f ebooks available right now (for maybe another week) through the latest Humble Bundle. What’s more, as per other Humble Bundles in the past, more books will be added as the timer counts down.
This “bundle” benefits the SFWA medical emergency fund and First Book, a program that puts new books in schools full of underprivileged kids, because god forbid we should ever fund education properly.
Check it out. Even if you are only interested in half the books, you’d be getting a good deal and helping worthy causes.