Mr Incredible...

ah beaten to it

Seen this posted elsewhere but found it quite funny

Keep em coming folks there must be a few more out there.

I'm sure you can find quite a few here:

http://www.worldsuperheroregistry.com/index.htm

Bouncing Boy from Legion of Superheroes, He is quite fat:

Captain Underpants!

Edit: Ahh, beaten to it. But I have a link!

Most Superheros are fat based on UN standards.  What being BMI based and all.

Additionally.  Big Bertha comes to mind.  Though technically she was a supermodel who's ability was to turn fat.

Of course the above bouncing boy is there too.

Personally I'd be more interested to see a fat character who's powers weren't based around being fat or the Earth element.

Whenever they do a 4 elements motiff... earth is always the fat one.

Gabe Newell

He makes Baron Harkonnen cry!!!   

How about Microbe from the New Warriors?

His power is not based about his weight, although it is not a cool one either: He communicate with germs. :S