Proper nutrition is a key component of any successful swimming regimen. Swimmers, and the people who buy and prepare their meals, need to consider their daily diet as well as their pre-swim and recovery needs. In general, swimmers need a diet full of lean protein, complex carbs and produce.
Here are some helpful resources:
USA Swimming's online Nutrition Center
USA Olympic Committee's Nutrition Center
Swimming.org's take on nutrition for competitive swimmers
SwimSwam's complilation of articles on nutrition