I have bought into the bicycling community tenet that if you bike everywhere, you don't need any additional exercise.
And this is mostly true. I am in excellent shape (for my age... and considering where I was 10 years ago...), but I've recently been looking to do more "core" workouts to atone for my rather sad midriff. Somehow 6,000 miles a year on the bicycle does not do a whole helluva lot for your stomach line.
So recently I've decided to start doing some exercises. I've started by doing just one after every commute. This is called "The Plank" and I find it rather good for tightening up the stomach.
Do you work out in any way... other than the bike?