Here is a collection of examples from the course Prototyping Interactive Systems
Design Challenge: Imagine you have a pressure-sensitive keyboard, where each key reports the character typed, and its press force, ie., how hard a person was pressing the key. What could you do with this keyboard? Create 10 different ideas of what you could do (it could be something useful or playful), and then choose one or two and create 10 variations of that idea and/or refinements of that idea.