Great, now I’m imagining it being spoken by Scooby-Doo:
“Ruh-roh! Chthuru!”
Of the Leominster Featherstonehaughs, or the Worcester Featherstonehaughs?
Talk about Dates Your Father Wouldn’t Approve Of!! 
That’s to be expected when you access the Interwebs using Pickman’s Modem.
Every person I know, including me, pronounces it ‘‘CUH - THOOL – WHO’’
Very similar to everyone else here, but with that hard ‘‘h’’ at the end.
It turns out it wasn’t Chthulhu, though, it was the boat captain, dressed up in a latex mask and costume. He would have gotten away with it, if not for those meddling kids.
He just told everyone he was of the St.-John Featherstonehaughs.
K’thoo-loo.
Until reading about how Lovecraft pronounced it a few years ago, I’d always considered it was pronounced K’t[sup]h[/sup]oo-l[sup]h[/sup]oo – the k being not a separate syllable but a /k/ sound prefixed to the /tu/ syllable, and the -th- being an aspirated t, not a theta sound – like “wethead” said quickly, if you will. However, the author gets to define how his names are pronounced – so all of us with /kth/ or /kt/ sounds are, so to speak, as cthuless as Alicia Silverstone’s movie.
priceless
Honestly, with my dad, the approval would hinge on how he voted. A demon-god who is a social conservative would probably pass muster, but demon-god who voted for dirty liberals? I’d be disowned!
I say cha-thoo-loo. It’s just one of those words I don’t really care how it’s supposed to be pronounced because whoever came up with it was being a jerk about spelling anyway. 
Who knows what’s correct, but I’ve always gone with: K-Thool-Hoo.
But the fact that the question was asked, is a testament to how cool this board is!
Ever heard of Beatallica? A Beatles/Metallica tribute band with lots of H.P. Lovecraft references? From “The Thing That Should Not Let It Be”: “…hybrid children watch the sea…”
K’thooloo. More or less.
Joe
k’THOO-loo. And not being a Lovecraft fan, it’s a term I only know from the Boards and doubt I’ve ever heard spoken IRL. Lucky for me, apparently, given the world-ending potential of the correct pronunciation.