If you want to find the minimised windows for a single application, you can activate app expose. This will show all windows, including those that have been minimised for the application you are currently using. Using BetterTouchTool you can link it to an easy gesture. I have my mission control as a 4 finger swipe down and app expose as the same but with the fn modifier key. Unfortunately it does not appear if there is a way to show minimised windows for all applications.