The Chaparral 2E
If there's one theme that you should pick up on in this list, it's that most cars get banned for messing with engine power or downforce. The Chaparral 2E is in the latter category. We've already talked about how spoilers increase downforce, which helps the car grip the road. However, there are times when you don't need as much grip and you want more speed. For example, when you're in a corner, you want grip. When you're on a straight, you want speed. Most spoilers split the difference, which means you give up some grip on corners and some speed on straights to have overall control. It's a trade-off most car racers are fine making.
Enter the Chaparral 2E. It had a moveable spoiler that the driver could manipulate. The spoiler could be put at a steep angle for plenty of downforce and grip in corners, then put at a less aggressive angle for the straight parts of the track, where less downforce is needed. As a result, the Can-Am racing series the Chaparral 2E competed in outlawed aerodynamic parts that moved.