Stashed in: Evil, gifs, Reaction GIFs!, Dr. Evil, Mike Myers, MRW, King of the Hill, Laugh!
That Jafar GIF is pretty sweet, but we can do better:
Hank from King of the Hill
Does this count as maniacal?
How about this one?
Oh! Found one! Army of Darkness!
Bonus points! Dr. Evil!
Dr. Evil's maniacal laugh dates back to his youth.
Al Bundy is laughing, but is it maniacal?