Saint Seiya's manga is written and drawn by Masami Kurumada. It has 28 volumes, published in Shueisha's Shonen Jump magazine from 1986 to 1991. They could be separated in 3 series and a interlude: 

1 - Sanctuary Saga

From the start to the battle against the Gold Saints in the Sanctuary.

Interlude - Hyoga's story

Hyoga's encounter with the Blue Saints.

2 - Poseidon Saga

Battle against Poseidon and his Marine Generals.

3 - Hades Saga

Vols 18 to 28. The last and better one, tells the story of the battle against Hades and his Specters. This one was never animated for problems between Toei & Kurumada.

Here you can download a summary & translation of this saga.

Tenkai-hen - The story never written

Masami Kurumada wished to write another saga, called Tenkai-Hen (Heaven's chapter), when the Bronze Saints and Athena confront Zeus and the Olimpic Gods. But Shueisha don't allowed him to, because they wanted another success story before allow him to continue Saint Seiya. But it's said Kurumada has not forgotten this project. 

Non-japanese editions

Spain: Planeta-de-Agostini edited the 18 first volumes, up to the end of Poseidon Saga. They was 83 issues, edited between may 93 and july 95.

France: Currently being edited by Dargaud.

Italy: Edited by Granata Press.

[Version en castellano]