I created this, inspired by a thumbnail sheet someone else made a while back:
...I decided to make my own version that suited the way I plan my comics. It supports only 12 pages, but one could easily print out or prepare more sheets to make more pages for a larger book. It focuses on showing which pages would face each other in a print book, and the guides on the sides of each frame allow for a number of general panel layouts or even a rule-of-thirds approach for covers and splashes.
I made it available as a .PSD with separate text layers for the Title, Chapter, etc. that can easily be modified or deleted as the user sees fit. Feel free to download and use to your heart's content if you like...no need to credit me or ask.