Greater Good: The Science of a Meaningful Life. This University of California, Berkeley site is full of great articles about gratitude and positive approaches to life. Sign up for the 14-day gratitude challenge and see if it makes a difference in your life.
Unstuck: A Practical Guide to Gratitude. Learn 9 ways to cultivate gratitude and discover the power of paying a compliment.
Gratitude Log. Bills itself as the happiest place on the Internet where you can connect with other grateful people.
Gratitude Works! By Robert Emmons.
Living Life as a Thank You by Nina Lesowitz and Mary Beth Sammons.
Help, Thanks, Wow: The Three Essential Prayers by Anne Lamott