You know that South Park episode with the gerbil Lemmiwinks? There's singing and music narrating his journey though Mr. Slave's innards. I like the catatafish part. It runs from about 1:40 to about 2:15 here (I already set the correct start time).

Can anyone recommend me more music like that? Something with that mystical atmosphere, deep choral vocals, chiming bells (aside from Black Sabbath, For Whom the Bell Tolls, Hallowed Be Thy Name, and Hells Bells), and/or dark slow acoustics? Metal suggestions are welcome, but I prefer they be in the genres of epic, heavy, power, doom, folk, pagan, viking, or gothic metal. I don't really like straight up death metal or black metal. Non-metal suggestions are also welcome.

In all seriousness you should look into/listen to Tenacious D. Sure it is comical, but it is precisely what you are looking for I think...

http://youtu.be/_lK4cX5xGiQ

That piece reminded me of "Epilogue" by Christian thrash/doom band Seventh Angel. As the title suggests it's the final track on an album ("The Torment").

And possibly the entire "Kveldssanger" album by Ulver, though that's probably a bit obvious? Maybe Of The Wand And The Moon's entire recorded output too. Neofolk is the way to go, I feel.

I think this one...

https://www.youtube.com/watch?v=u_tORtmKIjE

Hmmm neo folk does seem like the way to go here but if you want a nice blend with metal I highly recommend the band Sig:Ar:Tyr. Really great blend of acoustics and metal.

https://www.youtube.com/watch?v=abM9XcO ... D8980EFF49

Tenacious D is the band that comes to my mind too.

I also second Tenacious D. Also Ensiferum does alot of passages like this in their songs.

The best I could think of is Ulver - Bergtatt.

I hope this fits;