50 Press ups
50 Inverted rows
50 Seated knee raises
50 Upright rows
50 Shoulder press
50 Bicep curls
I came up with this as an upper body-only finisher when my knee was giving me problems. I tend to choose relatively light weights and go for speed. Even so, it's hard to feel as though your fitness is being taxed when there is no lower body work involved.
It borrows from the '300' workout insofar as you complete all reps of exercise consecutively rather than in multiple rounds. So this is a one-round circuit. You can make this as hard as you like by increasing the weight.
You can use dumbbells or a barbell for the last 3.
For the inverted rows, I prefer to use the smith machine.