A few books on developing leadership that were recommended at the AHG training at Philmont Training Center, August 2012.
The Student Leadership Training Manual for Youth Workers by Dennis McLuen and Chuck Wysong
One Girl Can Change the World by Claudia Mitchell & Kim Goad (best for Explorers and up)
Lead Like Jesus by Ken Blanchard & Phil Hodges (youth version forthcoming)
Leadership 101 by Denise VanEck