There is something very appealing about Desert Giant : The World of the Saguaro Cactus. The illustrations are lovely, and I had no idea how vital these plants are to the ecosystem in the Sonoran Desert (which is beautiful, by the way).
At the end of this book, my niece was begging, "Amy, can we please go to this desert in Arizona and see these cactus?! PLEASE???" My nephew was also engaged with this book, asking questions about the various animals that he was seeing, and even asking me what would happen if all of the cactus died.
This is a wonderful book that seems to really grab kids' attention. The book presents all kinds of learning opportunities, and it is very conducive to encouraging kids to ask questions and run with their curiosity. My niece gave this one five stars, and my four year old nephew gave it, "Ummm.... Sixteen!" :-)