Firstly, I have to acknowledge that the nature of gnostic phenomena is ALWAYS religious, because its goal has always something to do with SALVATION in religious sense. However, Gnosticism is a highly eclectic belief system and depends on a strictly DUALISTIC worldview. Many of its basic tenets, therefore, can easily be anatomized and considered as positions that stand on their own.
These positions maintain a radical dualism of realms of being, (God and the world, spirit and matter, soul and body, light and darkness, good and evil, life and death, etc).
Secondly, I think that only cosmological, anthropologic, (and maybe moral), tenets of gnosticism are manifested in the following songs. I don't claim that the owners of these songs were aware of the parallelisms that exist between the songs and Gnosticism, and this should not sound awkward. Remember that Shakespeare had no idea of Freud's theory of the Oedipus Complex when he created the character of Hamlet.
Among the themes frequently employed in gnostic narratives (and the songs in this list) are forlornness, dread, homesickness, fall, numbness, sleep, intoxication, the "alien man", the "alien god", light and darkness, "the beyond", "the without", "this world" and "the other world", "real love" and "blind love", etc.
Recommended reading for those who might be interested:
Hans Jonas -- The Gnostic Religion
Greil Marcus -- Lipstick Traces: A Secret History of the 20th Century
Jes P. Asmussen -- Manichaean Literature
Hans-Joachim Klimkeit -- Gnosis on the Silk Road: Gnostic Parables, Hymns & Prayers from Central Asia
Elaine Pagels -- The Gnostic Gospels
Joseph Conrad -- Heart of Darkness
10. Swans - Your Property
9. - Depeche Mode - Black Celebration
8. The Sisters of Mercy - Heartland
7. Swans - New Mind
6. Swans - Love Will Save You
5: Killing Joke - Love Like Blood
4. Public Image Ltd. - Theme
3. Swans - Mother/Father
2. Swans - Sex, God, Sex
1. Swans - You're Not Real, Girl