Eric Heberling did the music for the first two installments, Arena and Daggerfall. There's a reason there are dozens of music modifications for the later games floating around that replace Soule's works with arranged versions of the tunes from those older in the series, and it's not just nostalgia.
"Sovngarde" is pretty awesome by itself, but when it plays when you enter the Nordic land of the honored dead to do final battle with Alduin himself with the ancient heroes at your side, it takes it Up to Eleven.
Watch the Skies is unbelievably awesome, especially when fighting a particularly nasty dragon.
Secunda, one of the best ambient pieces in the soundtrack. Tundra is the other best ambient piece. A close third goes to Dragonsreach.
"We are the Dragonborn of Tamriel. We come from all corners, all places. From Skyrim, Morrowind, Hammerfell, The Summerset Isles, Cyrodil and all others. We are of all races. Nord, Orc, Breton, Imperiel, Elf Kind (Wood Elves, Dark Elves and High Elves), Khajiit, Redguard and Argonian. We are born in times of extraordinary crises. Tamriel will never fall into darkness. We the Dragonborn, the Dovahkiin will rise above all evil, vanquish it back into Oblivion. Always remember: Sky above, Voice within." -Youtube Commentator
Unbroken Road. It plays once in the entire game (specifically, when the ancient heroes banished Alduin the first time), and it is awesome.
Dragonborn adds to the game a bunch of new tracks, most of which are Morrowind remixes. They are amazing.
Forgotten Vale rivals the aforementioned "Wind Guide You" in terms of its larger-than-life scope.