For Fast Food Meals:
http://caloriecount.about.com/fast-food-restaurants-mc3
For Most Basic Foods (Not Brand Names):
http://nutritiondata.self.com/
For Many Brands and General Foods:
http://www.calorieking.com/foods/
Nutrition information on most brand name foods can also be found on the brand's website. Try searching the name of your food and the word "nutrition". For example, "Poptarts Nutrition"