There are lots of good books available. These two would be a good place to start.
Bibliography
General books on positive psychology/ happiness.
I don't usually use smilies, but I figure it is fair to make a bibliography a bit more lively.
Diener, Ed and Robert Biswas-Diener (2008) Happiness: Unlocking the Mysteries of Psychological Wealth. Malden, MA: Blackwell. One of the newest happiness books, this is a useful addition. Ed Diener is one of the founders and earliest researchers in positive psychology. His son Robert has been called the "Indy Jones of positive psychology" (some of the anecdotes from Africa and the Amazon will let you know why. This is very much researched-based but very accessible -- a good read. 
I guess it had to happen. Happiness for Dummies (W. Doyle Gentry, 2008, Indianapolis: Wiley) and A Complete Idiot's Guide to the Psychology of Happiness (Arlene M. Uhl, 2008. Alpha Books) have joined the pack. There is nothing particularly wrong with either of these. But most of the "... for Dummies" and "Complete Idiot's Guide to..." books describe things that are very technical and hard to understand such as computers, accounting, etc. There are lots of positive psychology books that are not techincal. I'd suggest starting with those (Lubomirsky, Diener & Biswas-Diener, Ben-Shahar or Gilbert are all good places to start). Having said that, of the two listed here, I found "A Complete Idiot's Guide" more interesting, perhaps because of the treatment of yoga and the physical aspects of being happy.
Lyubomirsky, S. (2007). The How of Happiness. New York: Penguin Press. Sonja Lyubomirshy's long awaited book. This is one of the best introductions to the topic. She makes the scientific basis of the ideas clear in a very readable way. She expands on the original eight ideas to include things like goal-setting and flow. This should be one of the first books to read on happiness.
Ben-Shahar, T. (2007) Happier. New York: McGraw-Hill. (This is a another good place to start). Tal Ben-Shahar teaches the most popular course at Harvard. This is the course text. An easy read with lots of good ideas.
Layard, R. (2005). Happiness: Lessons from a New Science. Layard is an economist and he approaches the topic from that viewpoint which makes the book interesting.
Seligman, M. (2002). Authentic Happiness. New York: Free Press. (This is another good place to start). Dr. Seligman also has a website at the University of Pennsylvania (authentichappiness.org) with many resources including a questionnaire that will let you identify your own “signature strengths”, preferences that lead to your own feelings of happiness and flow. 
Gilbert, D. (2007 -the paperback). Stumbling upon happiness. New York: Vintage. A fun, great read. Don’t miss this one. 
Niven, D. (2000) The 100 Simple Secrets of Happy People. New York: HarperSanFrancisco. (This is a “pop psych” book that summarizes applied positive psychology research and presents it in short, highly readable segments. Makes it easy to figure out the articles you want to get from inter-library loan.
Weiner, E. (2008). The Geography of Bliss: One grump's search for the happiest places on earth. Weiner is a writer/reporter for National Public Radio in the USA. He uses positive psychology research as a background for traveling around the world. This is more like really good travel writing than a positive psychology book but the stories make for a delightful read. Twelve.
Emmons, R.A. (2007) Thanks: How the new science of gratitude can make you happier. Boston: Houghton-Mifflin.
Seligman, M. (1998) Learned Optimism. New York: Free Press.
Haidt, J. (2006) The Happiness Hypothesis New York: Basic Books.
Kataria, M. (1999) Laugh for No Reason. Mumbai: Madhuri International. (For more on laughter, see the comments and links on the first Poster page)
Lyubormirsky, Sonja (2008). Dr. Lyubomirsky has a book coming from Penguin next year. I don't know the title. Watch out for it. Her work is really useful.
Articles
Hunkin, J. (2005) The Serious Business of Laughter. New Zealand Herald. May 1, 2005.
Lyubomirsky, S., Sheldon, K. and Schkade, D. (2005) Pursuing Happiness: The Architecture of Sustainable Change. Review of General Psychology, 9 (2). 111-131. (Dr. Lyubomirsky developed the list of behaviors on happy people. A summary of that work is here 
Many papers are available at Dr. Lyubomirsky’s website
She is writing a book on the topic that will be published by Penguin in 2008).
Lyubomirsky, S., Sheldon, K. (2006) Achieving Sustainable Gains in Happiness: Change your Actions, not your circumstances. Journal of Happiness Studies 7 (1). 55-86.
Seligman. M. and Csikszentmihali, M. (2000). Positive psychology: An introduction: American Psychologist, 55, 5-14.
Massage Therapy: Benefits of Massage. http://www.holistic-online.com/massage/mas_benefits.htm.
“Laughter is good for your heart.” (2000) University of Maryland Medical Center. http://www.umm.edu/news/releases/laughter.html
Rost, M. (2005) Generating Student Motivation. Paper presented to meeting of ThaiTESOL, Bankok Thailand. January 2005.
Helgesen, M. (2006) ELT and the Science of Happiness. The Language Teacher (Japan Association for Language Teaching). Available online at http://www.jalt-publications.org/tlt/articles/2006/07/index
Helgesen, M. (2005) Think Tank: Can we teach our students to be happy? http://www.eltnews.com/features/thinktank/042_1mh.shtml
Media resources: (some also listed on the LINKS page):
A BBC report on positive psychology/happiness. An excellent introduction to the topic.
Postive Psychology (Interview with Martin Seligman, Julie Norem and Mihaly Csikszentmihalyi. National Public Radio – Talk of the Nation. Sept. 23, 2002.
Happiness. Canadian Broadcasting Corporation – Quirks and Quarks interview with four psychologists on the subject of happines. Broadcast May 27, 2006.
Berk, L. (1996) The Science of Laughter. An Introduction. A National Public Radio interview. CD. Loma Linda, California: drleeberk.com
Murphey, T. (2006) 5 ways to happiness song podcast.
