What are the measurements of the different Lego instruction booklets? I've noticed that there are at least three different sizes (eg 7.8"x5", 4"x5.8" and 7"x8"). Are there other sizes?
Yes.
There are over 30 types, depending on box size. Some of them look more like books. Some of them are impractical, and haven't been reintroduced since their debut.