+1 for crossfit.
I just started doing Cross-Fit, the great thing about it is that every training session is different (I get bored easily) and you get results pretty fast. I also bike to work often, and I used to run a little.
Going back to the poster's question, the thing is, when you get older you have to do something or your body will not be kind to you. What has worked for me is to try something, do it for a while, and if I start to get bored, try something else. The secret to success is to keep trying. You'll start something, maybe you'll drop it (and that's fine), but when you do that, instead of giving up, just find something else to do.
If you are really that strapped for time, try running 20 minutes three times a week. At first, if you're out of shape, you'll walk most of the 20 minutes, but you'll get better pretty soon. One bonus of running is that it doesn't take much time (changing your clothes and maybe a shower), and you can do it pretty much anywhere.