1) Push Ups - 20
2) Overhead Raises - 20 (I use a kettle bell or a bag full of can goods/laundry/etc.)
3) Tricep Dips - 15 (A chair, couch or bed works just fine)
4) Basic Bicep Curls - 15 each arm (that kettle bell and bag-o-stuff works again!)
And repeat exercises #1-4 two or three times! I like this workout on days when I just don't have a full hour to get to the gym or just need a short pick-me-up workout.