At-home exercises for upper-body strength!

For full body workout check out http://www.nerdfitness.com/blog/2009/12/09/beginner-body-weight-workout-burn-fat-build-muscle This is the routine I use and you don't necessarily need dumbbells, He demonstrates in the video with a milk jug filled with water/dirt/concrete, anything to make it heavy for you. He also has some other workouts if this is too simple.

Upper body workouts: pushups, pull ups, chin ups.