Wow, surprised I get to see this on the front page of Hacker News. Gnostic sects are quite interesting. I've seen a good handful jaded ex-religious people who turned to Gnostic beliefs because of their dissatisfaction with modern religion, since they believe that Gnosticism is more "philosophical".

The Gnostics were hated during their times by the Neoplatonists for their over-emphasis on theurgy (religious rituals focused on awakening), and they were rejected by mainstream Christians after the first Ecumenical Council for being heretics (Gnostics believe that matter is intrinsically evil; orthodox Nicene Christians, in contrast, believe that matter is a "lesser good").

It seems that, from this article, Mandaeism also has some dualistic tendencies (believing that the world is a prison for the soul; and that the world was created by a god of Darkness). It's also quite radical to me that they consider Jesus, Abraham, and Moses to be false prophets, and that the Holy Spirit is an evil creature.

If you are interested in Gnosticism, you may be even more interested in simply reading the Neoplatonic philosophy of Plotinus and Proclus; or you might be interested in the early Christian theurgical writings of Pseudo-Dionysius and Maximus the Confessor. I think that these traditions are more internally consistent than Gnosticism.