While I do agree with doing cardio & diet for a significant difference,
you've already heard that.
Here's a site with a few new form & techniques that might allow you to mix it up a bit.
http://www.swiminfo.com/articles/swi...02swim_art.asp
I also like the torso swing (easy), and the lower oblique leg lifts (advanced)
While many believe the abdominal section's muscle group is different than any other,
in all actually, studies have indicate they are the same.
It's just there are not as many good focused forms for that area,
and genetics and lifestyle tends to allow more fat to build there.
(you use your arms & legs more vigorously than your lower torso)
Keep with the good diet (try cutting your intake down, it's not just the type, but the amount too),
I would try rowing as a cardio (that not that hard on the joints, and it's good for the abs)
And try mixing up with the new forms, your muscles get used to the same thing all the time.
Also simple situps & crunches only work the upper & mid abs.
You need it all (upper, mid, lower abs & front, side, back obliques)
Do not use much weight unless you want to build mass in specific areas.
Also, you might be having certain large stresses in your life,
it helps significantly on your body if you make an effort to reduce this.
Hope this helps