This printable reference is a comprehensive list of all possible formal divisions of a nine panel grid. Of course, there are infinitely more ways to divide panels once you get off the nine panel grid, but I've found it to be a great starting point.
Which is why this reference is cleanly printable as an 11x17 poster. Worth noting is that the first panel of each layout is greyed in for emphasis.
To nip it in the bud, I included all 322 possible layouts. YES, that includes a bunch that have an ambiguous reading order. Reality is a lot of people disagree on what constitutes legibility. So it's up to you to make educated decisions, and not draw pages that are hard to read. Maybe cross them out on your copy or something.
The dimensions for the poster are 11x17 at 300ppi.
A big chunk of credit needs to go to the members of the StackExchange thread that crunched the numbers to initally find the 322 possible layouts, with the math and justification to back it up. All I really had to do was organize them by number of panels and make it look pretty. Those initial contributors are:
Jaap Scherphuis https://www.jaapsch.net/