Gillian Welch - I Dream a Highway I listened to this album and only this album for about eight months. I simply didn't have enough love in my heart for anything else but Time (The Revelator).
Richard Wagner - Der Ring Des Nibelungen (around 14 hours) that's just the first part, but the whole piece is around 14 hours long, and worth every second.
Sigh - Lucid Nightmares (41:46) that too is only the first part of the song.