i dont like situps. ur abs are only used in the first 30 degree motion of situps which is basicly a crunch. for the rest u are using ur back, and as lazurus sed probably ur p-chain and hip flexors n stuff. but i have heard u can hurt your back from them and my back feels sore after doing theeom sometimes too. i prefer crunches. the burn is much better but make sure u do them slowly. russian twists ( dont try and do too many ) leg raises are good, pikes. that kind of thing. check out this abs workout i do, it works really good
http://www.bodybuildingforyou.com/tr...bs-workout.htm