Firstly, while the new album might not be the greatest, this song is easily a match for anything on anything outside the first five.
http://www.youtube.com/watch?v=3clLf-L9oSo

Secondly
Paranoid
Master of Reality
Volume 4
Black Sabbath
Sabbath Bloody Sabbath
Heaven & Hell
Mob Rules
Sabotage / The Devil You Know (as Heaven & Hell)
Technical Ecstasy

after that the others are only worth hearing as curiosities.