My favourite piece, bar none, is the Saga of the norn. I am not sure how often it is heard in-game but it features during the norn racial introduction.
If you haven't heard you can listen here:
When I get to the last 30 seconds my mind is filled with charging giants and the roars of shape-shifters, a bit like this.
And it makes me want to go and fight Jormag right now.
Hopefully I'll be back for dinner.