I love her vocals, the concepts of her songs, the often mid-eastern influence on her music, etc… I’d love to add more of this sound to my collection.
I’d suggest Lisa Gerrard and her old/returning band Dead Can Dance. She’s not as accessible as Loreena’s material, but she definitely has similarities. There is an almost other-worldly quality to her voice that is unlike any other that I’ve ever heard. I’d suggest the Dead Can Dance live album Toward the Within, her solo album Duality, and her collaboration with Patrick Cassidy Immortal Memory.
There are soundclips from all tracks on the provided links to see if they are up your alley. My favorites are “Shadow Magnet” (Duality), “Song of Amergin” (Immortal Memory), “Sanvean” (Toward the Within), and “Yulunga (Spirit Dance)” (Toward the Within).
Or you could just go for Enya 
Thanks- I’d never heard of her but I love the sound bytes. (Is the Patrick Cassidy from above the “son of Shirley Jones” P.C.?)
Heh, no
I guess he’s a pretty famous classical composer in Ireland.
You may also like the irish choir group Anuna. They have some really fun stuff.
Browsing the music downloads on Amazon.com, I came across “Å Ná (Arcane Chant)” by Suzanna Reeves. (I think that has only a 30-second sample; I know the full song is available elsewhere on Amazon). It has a Celtic/Gaelic quality to it kinda like Loreena McKennitt. You might like this one.
I second Dead Can Dance. You also might want to look up a little froup calle Trespassers William.
Korn.
I’m a huge fan of both Loreena McKennitt and Dead Can Dance.
My favorite DCD albums are Aion and Into The Labyrinth. I do like the live album, Toward the Within, recommended by interface, but for some reason i prefer the studio recorded versions of the same songs, maybe because i had those albums first.
I also like Lisa Gerrard’s work on the soundtrack to the movie Gladiator.
I can’t comment on Loreena McKennitt since I’ve only heard a couple songs of hers, but if you decide you like Dead Can Dance you might want to check out a couple of the following:
Vas
Mari Boine Persen
Marta Sebestyen
(ummm…I know there are some other folks who should go in this list, but it’s late and I’m blanking on them)
Some of the ethereal/darkwave/gothic stuff like you might find on compilations put out by the Projekt or Cleopatra labels
Dangit, I thought I was gonna get to recommend Dead Can Dance. Spiritchaser is probably my favorite album by them, but they’re all pretty wonderful. A Passage in Time is a relatively early “best of” album of their work.
Daniel
I ditto the “Vas” recommendation. The singer, Azam Ali, has her own solo CD out as well; it too is excellent.
PS. When Loreena starts touring again (supposedly next year?) I urge you to go, you will love it!
I have 2 Loreena McKennitt CDs and 2 Korn CDs in my car CD holder right now.
Maybe early Clannad, before they went all pop-like.
Anyone know why the big hiatus in McKennitt’s career? She had a string of very successful albums and then pretty much just stopped after the live double album came out in '97or '98.
Her live-in fiance, Ronald Rees, his brother and a close friend drowned in a boating accident in Lake Huron in 1998 and since then she’s done very little. Her Live in Paris & Toronto CD was a benefit performance for boating accidents. I hope she’ll release something new soon and resume touring.
As ever for such questions I will recommend Allmusic, one of the best resources on the web, which will provide a list of similar artists, influences, followers and song writers whose work she has performed.
You might want to try Lorenza Ponce. It isn’t Irish music, but some of it sounds similar to Loreena to me.
Connie Dover.
Some others that you might like:
Susan McKoewn
Clannad
Maire Brennan
Enya
A little different than LM is Jesse Cook…
He doesn’t come from the Celtic background. but has a World Music influence, especially on his last album “Nomad”. I think it would make you think of “The Book of Secrets”.
There is amazing musicianship in both camps, and as well, both are Canadian!