33. Superman vs. Lex Luthor (All Star Superman #12)
In the final issue of Grant Morrison and Frank Quitely’s All Star Superman, Lex Luthor has the powers of Superman (for 24 hours) and Superman is near death and powerless (after Solaris turned the sun red - the sun is now turning blue and it is major trouble).
However, Superman is a lot more than just his powers.
So first off, Superman (who seemingly died at the end of All Star Superman #11) comes back to life for one last battle, and his only way to fight Luthor is through a gravity gun and, of course, his wits, which are a lot better than people give him credit for.
While Luthor thinks he is on top of the world, Superman is secretly using the gravity gun to warp the time around Luthor, so that the 24 hour time limit approaches much faster than expected. As the powers run out, Luthor experiences the world as Superman sees it, and it almost drives him mad.
Now, Superman fights Luthor on the same level, and he naturally beats Luthor up badly, as Superman is awesome.
Superman is now almost dead (when he dies he converts to a sort of living solar energy), so his last act (after kissing Lois, of course) is to fly into the sun to fix it.
An amazing final battle for an amazing final issue of an amazing comic book.