Over the summer before my senior year in high school, I completed a summer-long internship with Mixzon, Inc, through the Saturday Academy Apprentices in Science and Engineering (ASE) program. I primarily worked on software development for a data processing application. I also did some web development, and helped with field studies. My symposium poster and presentation can be downloaded if you're interested in learning more about the internship.
If you are currently in high school, and are interested in science, math, engineering or technology, I would highly recommend that you apply for ASE! It is an awesome experience - you get to meet interesting people, learn new things, and it can be a lot of fun. For more information, visit the ASE website.