This anthem is sung by the one and only Dr. Doofenshmirtz in the episode of the same name, for the country of the same name...Doofania.
~~~
In the bay, off the coast of the Tri-State area
Floats a country for me, and me.
It's new!
It's bright!
And it's founded on spite!
And it's everything I dreamed it would be.
Hail, hail Doofania!
...
(During end credits)
There's a bright, shiny place
With a flag that bears my face
And it's floating on an inner tube
Far away from city life, my stupid brother and ex wife!
And it's got an evil attitude!
Hail, hail Doofania!