Just for the record, I think Ryven's post-apocalyptic zombie idea sounds like a lot of fun
Another idea I had was set around the theme of the Greek gods of Mount Olympus. The Hellenic gods and goddesses are lounging around their divine temples, feasting on grapes and ambrosia and enjoying the company of vestal virgins (gender of vestal virgins, of course, depending on the god or goddess in question), when--oh, noes! the almighty Zeus has been struck down! It turns out that a few gods, however, are not happy with playing second fiddle to the God of the Heavens, and have formed a secret fraternity called the Order of Othrys (named after Mount Othrys
, the barren peak from which the Titans were said to rule). The Order intends to free the imprisoned Titans and expel the rest of the Olympians into Tartarus!
Olympians = Roses. Their goal is to identify the usupers and banish them to Hades for all time!
Order of Othyrs = Thorns. Their goal is to depose the rest of the gods and rule Olympus!
Oracle at Delphi = Seer (this god has, among his/her worshippers, an Oracle who can see into the future and reveal the loyalties of another god)
Bearer of the Aegis = Guardian (this god possesses the Aegis shield of Pallas Athena, who can prevent the Order from felling a god and casting him into Tartarus).