This years FAR/AIM for starters. It comes on a CD rom for easy mailing.
Try the ASA people on
www.asa2fly.com - you see their books around most flight schools. I used the Private Pilot Test Prep and I guess they have one for CPL. Its for all flying machines but they have picked out the (H) questions for you.
FAA Flight Standards do the definitive "Rotorcraft Flying Handbook" which puts rotary into American vocabulary. You can buy it in most flight shops. (FAA-H-8083-21 is their book code.) Although it starts at PPL level it contains most of what you'll need at CPL and especially if you go to FI level.
My 2 cents.