Don't buy a book just because the things in it look easy to fold. Buy a book because the things in it look interesting and fun; many books start with easier models, so you can get up to speed, yet you aren't stuck with an entire book at the hats and dog's heads level. With perseverance and enough dexterity for decent precision (hm.. in a D&D system, I figure that'd be about 7 DEX) you can fold anything that has reasonably well-written instructions.
These are the books I have that I liked enough to take to college (which unfortunately means they're in storage at the moment with half my undergrad textbooks. Books are heavy!)
(I haven't written entries for the next four yet...)
Coming soon: a couple more books I've bought since then and actually have around at the moment.
These books are written in English and use the standard Randlett-Yoshizawa notation. (I have folded models from another book, which I don't own myself, using only the pictures; the text, originally Japanese, was an Italian translation of an English translation. Standard pictorial notation is sufficient, but text comments are often helpful.)
Several of these books mention the Friends of the Origami Center of America, "a tax exempt national organization committed to the sharing of paper folding". For more information it is suggested that one send a self-addressed business-size envelope with two (2) first-class stamps to "The Friends of the Origami Center of America, Box AB 15 West 77th Street, New York NY 10024". The British Origami Society is also mentioned in passing; I don't know anything about it beyond the name.