Bodyweight Exercises

A two cents worth for people that find themselves in a situation where they have to go out of town that they can't make it to the gym for a period of time (or people who doesn't have a budget for gym).

Here's Mike Mahler's bodyweight drill that is worth a try:

Handstand Pushups - 5-10 Reps
One-Arm Pushup - 5-10 Reps
Door Pull-up - 5-10 Reps
One Legged Squat - 5-10 Reps
Knee Jump - 5-10 Reps
Headstand Leg Raise - 5-10 Reps
Mahler Body Blaster - Work up to 25-50 Reps

Do check out Mahler's article for more details on this drill.