truth is exercises dont really change over time, just th eway you do them, i.e. gadgets and gizmos!
Any exercise that contracts the given muscle is good for that muscle, i.e. bicep curl for bicep, crunch for abs. Certain exercises give a higher intensity workout or are betetr for different areas of the smae muscle though.
for example a bicep curl with your wrists bent back takes the forearm flexors out of play and thus puts more load on the biceps.