For all music from a simpler time- much simpler- that you still find undeniably epic.
PS: I don't exactly see how dying en masse from Bubonic plague, getting bullied by local gentries, lords, and knights, and fearing that a dragon is going to snap your head off your neck or a witch is going to bubble your heart out your throat is considered "simpler", but whatever works. Dio was obsessed with it, and so is all of power metal, so there must be some humble allure.

And Blackmore's Night does qualify. Medieval doesn't mean only in medieval times.

I don't know how much music that's actually from centuries ago is going to be posted, seeing as there's not a whole lot surviving, but Falls of Rauros, particularly this song, always reminded me of a less complicated, easier time when nature ruled the land. Wyrd's Heathen evokes similar feelings for most of its duration.

I really enjoy these performances of early musical works (as well as the entire albums for these tracks):

http://www.youtube.com/watch?v=5-Cej8Kb5DE
http://www.youtube.com/watch?v=ccBpe0FpHr8
http://www.youtube.com/watch?v=robXU_chDTM

The Moon Lay Hidden Beneath a Cloud is the ultimate in medieval sounding music.

I always love when modern music has this kind of feel to it. I really enjoyed obsequiae's suspended in the brume of eos- metal chamber music in essence.

Of the wand and the moon, particularly nighttimes nightrhymes reminded me of this feel too.

It's a pretty basic thing but often it seems like vivid medieval imagery on album art helps a lot in creating this kind of atmosphere.

Pagan Alter give off a very ancient vibe... I don't think that's what you mean though. Godkiller are pretty cool for medieval thing.

Yeah, having the whole electric guitar thing, Pagan Altar are pretty wide of the mark. Unless I'm misreading things here, I think OP is talking about legit early music rather than even stuff like Dead Can Dance/Arcana etc, let alone BM or more Metal-orentated stuff.

On topic, I have a modest collection of Hildegarde von Bingen, various plainsong recordings, a few cd's of provincale trubador songs, and probably my favourite - an album called "Christmas at Saxon winchester", which is a combination of latin and anglo-saxon pieces.

I dig some von Bingen and Machaud. This is pretty old: http://www.youtube.com/watch?v=Wh6vVnWLvmU. I think it's a motet.