There are a lot of books about Pokemon, from what I've been able to find. Those are always helpful...then there are a few that give more information about the regions here, Johto and Kanto.

[Kanto has been a favorite of his lately, since he doesn't think he'll actually be able to travel that way any time soon.]

There is a bookstore in Goldenrod City that I work at that has a lot of different books to choose from.