Originally Posted by
QRH Bingo
Plenty of online courses to take which prepare you for the written test; sportys, gleim, kingschools... If you wanted a book, The Pilots Handbook of Aeronautical Knowledge and The Airplane Flying Handbook is a good place to start.
If you're planning on training at a specific school, find out which course they use. Otherwise, pick one. The FAA handbooks are great as reference and also as light reading to get you started, but the structured courses will better focus you for actual training (and written prep).