This isn't a spoiler in the "Here's What Happened" way. It's a spoiler that will ruin the movie for you:
"Voice Of Sauron" performed by Kenneth Williams.
You could cast all of Carry On Up The Ring (Sid James as Aragorn, Hattie Jaques as Arwen, Frankie Howerd as Gandalf) but I think it's enough to imagine Sauron saying "I say,you there! Build me an army worthy of Mordor, you silly boy."
There. Spoiled it for you.