This is a great question. It is probably best to define what Aspartame is first and then proceed to talk about what foods contain it. Asparame is an artificial non-saccharide sweetener that is used in many foods and beverages. It is abbreviated as APM.
APM is found in Equal, NurtraSweet and Canderel. This alone should tell you that Aspartame is ubiquitous. According to one study, APM is found in over 6,000 consumer products.
With this said, it is important to note that APM is not without its controversies. Many people have complained about its health dangers.
As for foods that contain Aspartame, I will name some of the more surprising ones: breath mints, chewing gum, fruit spreads, gelatin, instant coca mixes, jams and jellies, maple syrups and sugar free ketchup. To get more examples, all you need to do is to read labels at the supermarket.