Tiresias's Clique: Seers
Tiresias is one the most famous members of this group that 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 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.
Oracle of Delphi/Apollo
The Oracle of Delphi was the place to go in ancient Greece if you wanted to get a little peek into your future. Usually, one young girl acted as the prophetess. Her duties included hanging out in a temple all day, inhaling volcanic fumes that drifted up through the earth, and having crazy trippy trances in which people believed she could catch glimpses of the future. The Oracle was a temple of Apollo, the god of prophecy who was said to be the guy sending the visions. It's said that Apollo claimed the Oracle—which used to belong to Gaia, the Earth—after killing Python, Gaia's son, who also happened to be a giant snake. Oh, Greek mythology.
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 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.