futurecatcher,
Jon is right on with his advice...stay away from crunches and focus on exercises and movements that strengthen the core WHILE performing other movements. Very rarely should a person with correct posture and an otherwise unremarkable medical history, be performing specific work for the core musculature (ie. crunches, jacknives, leg raises, etc.). All these exercises serve to accomplished is to attempt to isolate the core, which A) is impossible and B) is counter-productive to your overall physical development. When you squat, push, pull, bend, lunge, twist and perform gait, you want your core supporting and stabilizing your entire body throughout all of these movements.
If you want to test this out for yourself or if you get questions from fellow teammates, have them perform a squat session performing only front barbell squats with about a 4Rm to 6RM (depending on your age). Ask them how their abs feel...particularly the rectus abdominus the next day (the six pack muscle)! You'll often find that you're more sore in the abs the first time you try this than you ever were peforming thousands of crunch-type movements.
Dave