musky is abolutely right. you can do all the ab exercises you want and it won't matter.. you can't spot train to lose fat. you have to lose your total body fat to see the abs in the first place
now once you do get there i think situps are wonderful. there is nothing wrong with situps, pushups, pullups, dips, etc. these stratic exercises using your own body weight are excellent. why do you think guys who do advanced yoga are so ripped?