Here's another workout that doesn't require any equipment. If 50 reps is too tough, start smaller and work your way up. Time yourself and see if you can improve the next time you do it!
In celebration of the start of the CIA summer workout free swag bribery contest here's a Superman themed body weight workout:
That website (http://neilarey.com/workouts.html) has all sorts of different themed workouts, so if you're looking for something fun to do to earn points, check it out!