For time:
100 Pull-ups
100 Push-ups
100 Sit-ups
100 Squats

Complete all of one exercise before moving on to the next (i.e. you have to finish your 100 Pull ups before moving onto the push ups – and yes!, they are gold standard push ups [wmv][mov])

To scale, either drop the amount (e.g. 75 of each exercise), or use modified exercises – jumping pull ups or incline push ups.