Page Proportionsby Christoph Koeberlin
Not only the size, but also the page proportion is decisive for whether a book is perceived as pleasant. In Bücher machen (see also the Typographic Canon), Jost Hochuli lists some tried-and-true page proportions. According to Hochuli, books that are held with both hands or placed on the table may be proportionally wider than small ones for holding in the hand.
If you like it more detailed or want to approach proportions musically, you should definitely read Robert Bringhurst. And those who are looking for exact formats instead of proportions will find what they are looking for in paper sizes.