George Lopez hosts a countdown of the 20 hottest TV happenings of the year, as chosen by the editors of TV Guide. Among the top eyepoppers: Madonna and Britney's MTV lip lock; the premiere of "Queer Eye for the Straight Guy"; Frankie Muniz's "Punk'd" prank; and Arnold Schwarzenegger's gubernatorial announcement to Jay Leno. Also: a look at trends among teen shows; the world of reality TV; and the year's guiltiest pleasures.