If you are one of the many people who sit at a desk all day, using a recumbent or regular bike for your workout may not be your best bet. Instead, try an exercise like running or soccer that gets you into an upright position and stretches out your muscles. Working out in a different position than you are accustomed to prevents the aches and pains that result from being in the same position all day.
To develop great looking abdominal muscles make sure that, in addition to isolated ab work, you include heavy free weight compound exercises in your training. Basic old-school lifts like squats and dead-lifts are great exercises to build your abdominal muscles because during these lifts your abs are forced to contract in order to maintain proper posture.