CFI requires a lot of books and materials, but for starters get an video set of some sort like ASA's CFI set and also get a Gleim pc-based or paperback testbank and work through the practice tests until you make 90+ on practice tests.

[EDIT] Here's a more complete list, in no particular order. I have most of these but find that most do not receive regular use. I read them and store them in the back of my head for future use as needed. By the way, Jedi Nein' s list (see her link) has some important items not mentioned here also.

FAA AC 61-98A Pilot Currency
FAA AC 90-66A Airport Traffic Patterns
FAA AC 61-67 and 61-67C Stall/Spin awareness

FAA AC 00-6 Aviation Weather
FAA AC 61-65E (replaces 61-65D) Endorsements
FAA AC 00-45 Aviation Weather Services

FAA-H-8083-1 Aircraft Weight & Balance Hbk
FAA-H-8083-9 Aviation Instructor’s Handbook
FAA-H-8083-25 Pilots Handbook of Aeronautical Knowledge

FAA-H-8083-3A Airplane Flying Handbook
FAA AC 61-21 Flight Training Handbook
FAA AC 61-91H Pilot Proficiency Award Wings

FAA AC 90-42F Radio Procedures
FAA-H-8083-27 Student Pilot Handbook
PTS for the Private, Commercial & CFI certificates (made by ASA)

AOPA Instructional Safety
local Airport Facility Directory (AFD)
ASA CFI Oral Exam Guide

ASA Visual Flight Maneuvers Handbook
FAR/AIM 2004
Jeppesen Private Pilot Manual