Oracle of Delphi (The Pythia)'s Clique: Seers
The prognosticating Oracles of Delphi are some of the most respected members of this group, which spends all its time at lunch with tarot cards, crystal balls, fortune cookies, and, most importantly, astrology books. If you want to get a hint about what's on the horizon for your life, these are the people to ask. But you'd better think twice before you start looking for answers. The truth is, you might not like what you hear.
Cassandra
Cassandra is a pretty unlucky member of this clique. Sure, she's a really pretty Trojan princess and was granted her prophesying powers by Apollo, but she's also horribly cursed. See, Apollo was sweet on her; and when she rejected him, he cursed her to never be believed. So she can see all the doom on the horizon for those around her, but whenever she tries to tell them how to avoid it, they just think she's nuts.
Tiresias
This blind prophet of Thebes can see into the future like nobody's business. His main method of divination is through augury, the art of predicting the future through the flight patterns and songs of birds. He can also divine the future from the smoke of burnt offerings and even receives visions straight from the gods. This prophet of prophets shows up in tons of ancient Greek tragedies and is most famous for his role in the Oedipus plays.
Chiron
This gentle centaur is a killer prophet and can tell the future from the movement of the stars. He also happens to be married to the nymph Chariclo, Tiresias' mom. Besides being an awesome fortuneteller, Chiron is also a famous teacher of the stars (the famous human kind, not the glowing things in the sky). Achilles, Jason, Ajax and many other legendary heroes all call this half man/half horse "teach."
Mamitu
Mamitu is a Mesopotamian goddess who lives in the Underworld and knows everyone's fate. Of course, she's also the one who decides everyone's fate, so maybe her prophesying ability isn't quite as impressive as it sounds.