I second everything Jack said. I have my gym in the back yard. I have no excuse in terms of time. Finding a program that is fun is crucial as well. In terms of a sport, that is what got me back into it as well.
Several years ago I wanted to take up tennis again after a layoff of a number of years. In looking for grippers and other hand and wrist strength info, I can across www.ironmind.com
. THat sight inspired me to take up olympic style lifting and strongman type fitness.
I just took up throwing the javelin. After being put in touch with the strength requirements for that sport and after throwing on my own, I have discovered (thanks Jack) an entirely new set of exercises and workout routines that will keep my busy and sore for quite some time. If you like DVD's and video's, ironmind has strongman videos that should really get your testosterone pumping. Reading books and articles about old time strongmen is a never ending source of inspiration for me.
Keeping up with my boys is a huge motivation as well. Kids are getting bigger and stronger faster, I swear, than when I was young. I need to stay in shape to keep them in line:-) Just being able to play with them and keep up with them through their teen years will take alot of fitness on my part.
If you have a competitive streak, nothing puts the fear into you like actually signing up for some event. That gives you a deadline to train for. Three years ago I bit the bullet and signed up for my first triathlon. All of a sudden finding time to swim, ride, and run became a priority.