I know I already told everybody about running errands with your bike, but lately I've started commuting with my bike, and I am amazed with the results. Not only I get my exercise done, but I also save and average of 40 dollars a month, just in gas!!!
The hint here is to workout without even realize it! Plan different things to do, like a day skiing, or snowshoeing, going on a hike, or a historical tour of your city. Make something different and fun, and you will exercise without that feeling "I have to workout"...
Run errands riding your bike if you can (even grocerie shopping). The amout of gas you save is amazing! I've been doing it for a while and I am really satisfied.
And you save money by getting a workout without having to pay for a gym.