We all need exercise but there are cheaper and more environmentally friendly ways to exercise than the gym. If you quit the gym you will not only save money from the membership but also from the gas you burn driving to and from the gym.
If you normally run or walk on the treadmill or elliptical machine at the gym 1-2 miles a day take your car for a drive one mile from your house and see what stores you pass. You can walk to all those store to get what you need without having to go to the gym or burn the gas to run your errands. It will not take you anymore time (and it could be arguably less time) to walk and run errands than it is to go to the gym. You can also take your kids or dog on a long walk more regularly because you do not have to compete with the gym schedule to get everything done.
If you lift weights you can do yard work (if you have one) or you can walk home from the grocery store carrying your bags. If you really feel that weights are important you can still get weights for your house less than a few months of membership at the gym and you have it forever.
If you ride the bike… buy a real bike and you can go even farther than walking to run your errands. Get a good backpack and you can ride around town and get your errands done. Your bike riding workout will likely be even better on a real road with actual hills.
If you stretch or do yoga you can still do that at home with a video or even the Wii Fit.
Another way to stay healthy is to play sports with your kids at the local park. You can get a softball game together pretty quickly with a few kids. You can play catch, kick the soccer ball around or even play tennis or racket ball against a brick wall (I used to practice tennis as a kid at the school down the street hitting the balls off the wall of the school).
Time are tough economically and this a great way to save money, stay healthy, and help the environment.