[helterskelter]

I've heard good things about openstax.

[nosioptar]

I used several of their books in school. Each of them was top notch.

Hell, their math books are better than the paid books I used.

[helterskelter]

I'm glad to hear that, I just ordered their astronomy book the other day! The online/PDF material looked good but I hate diving into something unless it's on paper.

[nosioptar]

I've seen a couple printed books from them. They all seemed to be a pretty good quality print.