Diablo & Diablo II — Tristram.
The rest of the soundtrack wasn’t exactly bad, just very very subtle and low-key. This song is incredible, though, and if they put a variant of it in Diablo 3 that uses electric guitar instead of acoustic guitar because it’s more hardcore I am going to hop on the next flight to America and murder everyone at Blizzard.
You will be pleased to hear then that they have used an only slightly altered and very good rendition of it in Diablo 3!