Doing things like getting married, exercising, and even voting can increase happiness levels. A UK report finds that people are more satisfied with life when they participate in democracy, among other findings.
"The Politics of Happiness." Ollie Stone-Lee. BBC News World Edition [Internet] 20 January 2003. Available from:
http://news.bbc.co.uk/2/hi/uk_news/politics/2670263.stm

More Happiness = More Sex. A study aimed at quantifying the links among income, sex, and general happiness found that married people have considerably more sex, and the "happiness maximizing" number of partners in a given year is almost exactly one.
"Money, Sex & Happiness: An Empirical Study." David B. Blanchflower & Andrew W. Oswald. Scandinavian Journal of Economics
http://www.dartmouth.edu/~blnchflr/papers/sentScanJEsexmoneyhappinessjune2003.pdf

Turns out that people can decide what kind of relationship they want within minutes of meeting. In short, this is proof that love at first sight exists. Romantics rejoyce!
"Proof love at first sight exists." BBc news. Available from:
http://news.bbc.co.uk/2/hi/health/3643822.stm

Will getting married make you happier? A new study suggests no, in contrast to previous research that has said that married people are happier and healthier. What scientists are learning is that the people who get married and stay married tend to be happier than people who remain single. Read more here:
"Is There a Hitch?" Joel Stein. Time Magazine 17 January 2005: A37-A40. Available from:
http://www.time.com/time/magazine/article/0,9171,1015873-1,00.html