[yamtaddle]

There's also the famous Harvard Classics, or the 5-Foot Shelf, sold as a kind of primary-sources curriculum, complete with a reading plan:

https://en.wikipedia.org/wiki/Harvard_Classics

A Great List of Great Book Lists:

http://sonic.net/~rteeter/greatbks.html

[EDIT] On this:

> Also, almost all of these books are old enough that their copyrights have expired so you can download them for free from the Gutenberg e-library: https://gutenberg.org/

I'd caution readers to also evaluate in-copyright editions, especially in the case of works in translation. Used books are cheap and it's worth getting the best possible translation (however one chooses to evaluate that) if one is going to spend hours with it.

And:

> One feature I've wished for is some way to format these free books and make them more reader-friendly. That would save future readers time to do it themselves. I would pay for something like that.

Standard Ebooks?

https://standardebooks.org

Not comprehensive, but they've got a lot.