Twenty Minute Squat Workout

Take a weight that you can handle (60 - 70 % of your one rep max if you're doing weights) and see how many reps you can get in a twenty minute sessions. Repeat this workout every couple of weeks and always aim to beat your previous max. I do this with squats, and pull ups. The squat workout will boost your metabolism like crazy.  

Sprints

This one is affordable but not easy. Pick a distance, it could be 50 yards or 100 yard. You want to jog the first one, run the second a little faster and by the third or fourth sprint you should be hitting a good stride. You want about 1 minute or 2 of rest between each sprint. Maybe a bit longer for the 100. Keep the sprints going as long as you feel you have a chance of topping your best time.

Drop Sets

I'm not a HIT guy but I like to throw in a drop set here and there. One set and go for broke. Do a heavy weight 4 - 6 reps, and then take 20 -30% of the bar and rep out. This is a good way to get in another exercise without using up to much time.

Bodyweight

Get outside, do some lunges, pushups, etc. Do a handstand against a tree, run some stairs, whatever comes to mind. This will keep you from being tight and a good way to motivate yourself to stay lean. The leaner you are the more bodyweight exercises you can do.

Compete at Something

Find an event and enter it. It could be as diverse as a  bike race, 5k, 10k, weightlifting/power lifting contest, or team sport. Golf and bowling don't count. Make your workouts compliment something tangible and athletic. If working out is just something you do because your doctor told you, or you think it will make you look better, you're not really "getting it". Put yourself out there in an environment where you are having fun, but pushing yourself harder. That isn't going to happen if workout dvd's are the pinnacle of your athletic existence.

Just a few ideas to start with, more to come....
Tom Pollard