More muscle stomach - Tips?

I've been acting normally until recentely I've thought: "I'm not that strong and don't want to get pushed around in school anymore, what can I do to make my arms and body stronger?"
I've got weights which I use to do regular excercise. I'm just wondering what I can do to get my stomach muscles stronger.
Anything apart from crunches and sit-ups?

Thanks.

Here's a good few ways;

http://www.wikihow.com/Get-Six-Pack-Abs

GYMBALL. SITTING ON THEMM LIKE TENSES YOUR STOMACH MUCSLES. [:

thanks for the advice guys, anymore?

... Situps? Hate to break it, but that's the only thing really.

All other exercise for the stomach area is based around situps or the structure of one.

CRUNCHES!! seriously, they're amazing, Like do 20 at a time,
http://www.youtube.com/watch?v=d_KRHFuVvrY
http://www.youtube.com/watch?v=LJ6y2ySAkmQ

If the link doesn't work copy and paste, I do them xD
I used to do sit ups and they're bad for your back.

thanks guys, i've +repped all useful information.