not to take away your motivation, but some people like my brother just can't get rid of the little gut. I mean even Chuck Liddell has a little chub on the bottom of his stomach, even at the weigh-ins after cutting a lot of weight while the rest of his body is ripped, he calls it his power gut.
also, sit ups don't do much for you lower abs, just google a lower ab routine. You need to switch up the type of excercises you're doing so that your muscles don't become complacent
also, you are doing way too many repitions. Ab excercises, more than any other part of the body is all about quality repitions over quantity. There is an entire article about it in the latest issue of "Muscle and Fitness" magazine. It says if you are doing over 20 reps per ab excercise you are doing it wrong. You need to add resistance (powerbands, holding a weight plate on your chest, or have a buddy pull against a towel that is wrapped around your chest while you are doing them)
finally, make sure you aren't just going through the motions, you have to focus on flexing your abs as hard as you can. Breathing is also key, say your'e doing sit ups, you want to exhale on your way up, and inhale on your way down. This because your abdominal muscles will contract a lot further when there is no air in your lungs giving you better results.
good luck man, ab training is by far my least favorite part of going to the gym, but its so necessary.