It may not be the most epic song that I've heard (and might not be classified as epic to most people), but Sectoid - Feelings is the best one that I can think of right now. I absolutely love it. It's also a lot of fun to play on Frets on Fire, and I believe it was even made just for that, too.

Another one that I love is the Morrowind theme. It's one of my favorite pieces of music, maybe even my favorite.

Its gots to be the cheeky Girls ;)

Status Quo- In the army now

The Last of Us OST - The Path (A New Beginning)

Totes

What 's new pussycaaat woaaah woaah woaaaaah

for me it has to be this

and also Cult of Personality

Chelsea Grin - Recreant

"Suicide Mission" from the Mass Effect 2 soundtrack; the version played by the London Orchestra.

Dies irae from Verdi's Requiem

Ara Batur by Sigur Ros

I'm a sucker for the long drawn out climax but the last 2 minutes are phenomenal.

This song - Some People

Mozart piano concert: Clicky

Also, did you guys liked this game soundtrack?: Clicky

The game is still fully free on Origin (not demo) i think: LINK

My favourite song of all time. Always gives me the goosies at the first drop.

Devin Townsend Project - Supercrush!

Just this

For me, it's this Clicky

How could you miss this, guys? -Yoko Kanno - Inner Universe-

Omnium Gatherum - Soul Journeys

There Were Roses, by Tommy Sands

(I was introduced to this song as performed by Gordon Lyons of Wild Mountain Thyme.)

Most epic? How can it not be

THIS

Absolutely impossible to name one song. However, for me most likely none of the ones mentioned (didn't read).

Icarus

Johnny Cash - God's gonna cut you down.