One of the questions asked of a team of Columbia University health educators and health care providers -- had to do with which foods put the mood-altering chemical into a person's system. The answer cautions that attempting to raise serotonin levels through eating alone is tricky, because people often react differently to similar foods. However, the site states:
Carbohydrate-rich meals often increase serotonin levels... Believe it or not, candy and sweets, which are simple carbohydrates, have the greatest impact, but the effect will only last 1 - 2 hours. Complex carbohydrates (rice, potato, pasta) may increase serotonin levels, but not to the same extent because the protein content of these foods might actually inhibit serotonin production.
I headed back to the search results for more details. I wanted to find some specific examples of foods that increase serotonin levels.
An article on how food alters your mood from ParentsPlace.com suggests that carbohydrates trigger the release of insulin into the blood stream, which clears all the amino acids from the blood, except tryptophan. When competitors are out of the way, the tryptophan floods the brain, where it's converted to serotonin. Whole-grain breads, crackers, pasta, rice, cereal, and fruit all have the potential to increase your serotonin level.