Ooooh, my turn!
It's probably a safe bet that "epic" is one of my favorite genres of music, Providing that it's not "generic epic" like I've found a lot of film music lately.
Keywords: "One Of" my favorite genres. I have very much enjoyed many pieces of music which are a long way from the "epic" category...but that's another topic

What is "epic" music? I always found it to be more of a "feel" than a concrete definition. I've been asked before what I considered to be "epic" music. The problem is that my definition of "epic" music doesn't seem to coincide with the generally accepted definition of "epic" music completely.
Artist - Title - Length of the song
Nightwish - Ghost Love Score - 10:01
Nightwish - Creek Mary's Blood - 8:29
Sonata Arctica - The Power of One - 10:01
LBT Soundtrack - Rescue, Discovery of the Great Valley - 12:46
LBT Soundtrack - Sharptooth and the Earthquake - 10:35
World of Warcraft: Burning Crusade - Opening theme - unknown length
The Lord of the Rings - Any of the major themes - unknown lengths
Trevor Jones - Dinotopia: Pteranodons - 5:31
....
You know, this is interesting! I have been looking through my (25 GB) music collection for some time and I can't find many tracks that, when I really think about it, would be considered "epic". Perhaps pure "epic" music isn't one of my favorite genres but other musical styles with epic touches (memorable themes, full sound) are more appealing; I can think of quite a few more of those:
Turok 2: Seeds of Evil - Level 2 soundtrack - 4:56
Dreamgale - Fortress Guard - 4:15
Donkey Kong Country - Ambient Gemini (Water music remix) - 3:57
Donkey Kong Country 2 - Stickerbrush Symphony - 2:18
Donkey Kong Country 2 - Brambles in the Breeze (remix of Stickerbrush Symphony) - 5:32
Donkey Kong Country 2 - Forest Interlude - 3:04
Kamelot - The Coldest Winter Night - 4:03
Linkin Park - In The End (I don't know why but I like this song) - 3:36
Kamelot - Abandoned - 4:06
Unknown artist (Initials: J.A.) - Fish out of Water - 2:22
Holst - The Planets (Venus and Neptune, specifically): - Combined time: 17:27
John Williams - Helicopter Ride to the Island (Jurassic Park) - unknown time
James horner - If We Hold On Together (and variations of this theme throughout the LBT soundtrack) - Length varies.
Whoops, I just realized this topic is for Epic "SONGS". heh...is it okay if I post tracks that don't have lyrics?

:
As for some "rock epic" songs which I enjoy that have epic atmospheres about them, despite their tougher exteriors:
Kamelot - Momento Mori - 8:54
Kamelot - Descent of the Archangel - 4:35
Nightwish - Planet Hell - 4:38
Sonata Arctica - White Pearl, Black Oceans - 8:46.
Nightwish - Beauty of the Beast (not "Beauty and the Beast"

) - 10:02