If you are just beginning to learn about soaring, Hollister Soaring Center provides training with fantastic CFI-Gs. They will cover everything from your introductory flight to your certification. They offer an accelerated course for new pilots, usually spanning 6-8 weeks, and one for transitioning power pilots spanning 2-3 weeks.
Russel Holtz provides excellent introductory material for learning to fly gliders. The volume Flight Training Manual for Gliders covers flight training, while the Glider Pilot’s Handbook of Aeronautical Knowledge covers the knowledge training. They cover all topics required by the FAA from your first flight to the Bronze badge. The material is very clearly presented with easy-to-read figures and explanations. Start here!
Private Pilot Glider Practical Test Standards (PTS) - FAA 2011. The PTS establishes the standards for private pilot certification practical tests for the glider category. FAA inspectors and designated pilot examiners shall conduct practical tests in compliance with these standards. Flight instructors and applicants should find these standards helpful during training and when preparing for practical tests. This is the material from which the examiner will pull his questions.