I have to say cycling, which I got into seriously this summer as part of a fundraiser for the Leukemia & Lymphoma society, has been absolutely the most effective exercise I've ever done. I've ridding two centuries now, and ride 50-150 miles per week on the road, plus a few hours every week or so on mountain bike trails near my home in Marin, and it's gotten me in fantastic shape.

I've been a walker, hiker and snowshoer - and occasional skier - for years, and while those have kept me reasonably fit, none have done it as quickly and effectively as riding the bike.

That said, to go back to the original question, it may not be the most bang for the buck (walking and calisthenics no doubt are), but a cheap garage sale or Craigslist bike can get you going pretty cheaply. You can also use it instead of the car for nearby errands and trips - a double bonus.

Heh. I just read this after your hunting thread, and thought that "best bang for the exercise buck" was about looking for the best weapon to use against some sort of triathlete male deer.

Exercise buddy or two.

An active game you like and some kindred spirits.

Go fishing, visiting, shopping, out to eat in a rowboat.

Getting a dog increased my daily walking, reduced my stress and gave me more quiet time with my wife while walking the dog.

Jeff

Hiking is mine. Better for the knees, hips and back than jogging, although you need more time for the same results.

And it isn't hard. If it is, say, five miles to the mall and you need go there this weekend, grab a pack. Walk. Walk around the mall, browse more than you would normally. Skip the food court. Walk back. Yes, it adds a couple hours to what might have been an hour errand. Even if you don't have the many hours, pick a central location to park if you have a number of errands within a mile of eachother.

+1 on the cycling, but try a recumbent style bike. Much, much more comfortable and the same workout. I now have both a recumbent cycle and a recumbent exercise bike.