• Psych Central: The relationship between Happiness and Gratitude
• The Blog at Huffpo: Scientifically Proven: Gratitude is the Gravity Quotient of Happiness
• How stuff works
• A paper on happiness and gratitude

“The worst moment for the atheist is when he is really thankful and has nobody to thank”: Commonly attributed to Dante Gabriel Rossetti but the citation has never been documented. It is found written by GK Chesterton in St. Francis of Assisi (1928)