What are some of the best free ebooks available online?

Project Gutenberg is a great resource for free books, but its 50,000+ titles are intimidating in number (if not outright impenetrable). The same goes for other free ebook aggregators/feeds, of which there are many. There are also lots of authors who offer up their books for free. And, of course, there are tons of free options available in, say, the Kindle store. While it's nice to have so many choices, it hinders discoverability. Individual books get lost in all the noise.

As such, I'd like to know: what are some standout, recommended books that are available to readers for free?

Obvious disclaimer: I am not interested in pirated content.