The Complete Idiot’s Guide to Book Proposals and Query Letters by Mary Allen and Colleen O’Shea.
Since I’m in the process of preparing my manuscript for (eventual) submission, it’s good to keep researching how to do it. It lists online resources for writers and includes a ton of tips about getting the reader’s attention by including sample letters.
 
Under the Mesquite by Guadalupe Garcia McCall.
This book is written in prose poetry form. It’s about a teenage girl named Lupita who struggles to deal with her mother’s battle with cancer through high school. It's a heartwarming story.