What can you say about the album that started it all? It's fair to say that without Black Sabbath, the majority of the other albums in this Top 50 would not exist.
The band, the album, the song: the unholy trinity, diabolus in musica and the root of all that's brilliantly evil in heavy metal music.
“Black Sabbath - Black Sabbath. The title song is the scariest thing you will ever hear. Heavy metal is all about playing a power chord followed by its flat-fifth and they did it first.” (Thanks, vivekayer)
"Black Sabbath - Black Sabbath (1st album)." (From Fotis via Facebook, thanks)
“Black Sabbath - Black Sabbath... the origins???” (Thanks, mdg1157)