When it comes to epics, the Shahnameh (also known as the Persian Book of Kings) is definitely one of my favorites. I have loved it since I read some stories from it in an abridged "Epics of the World" collection back in middle school.
The Shahnameh is the national epic of Iran, the history of their kings from mythic origins all the way to the 7th century. It was written in verse at the turn of the 10th and 11th centuries by the poet Ferdowsi, who based his work on much older sources, tales and legends. The book contains some of his notes, comments, and musings about his own life during the thirty-something years he worked on it.
The Shahnameh exists in a number of English translations. I bought the 1967 Persian Heritage Series volume, translated by Reuben Levy - mostly because it is lavishly illustrated with miniatures. It turned out to be a very hard read, since Levy wanted to reflect the archaic language of the epic by putting it into Shakespearean (prose) English. Also, he annoyed me by cutting some of the best mythical parts out of the story, calling them "fanciful tales." I ended up re-reading the missing parts from the newer edition translated by Dick Davis.
The center of the epic is a long line of Iranian kings. Some of them, especially in the legendary eras, get more detail and attention than others. The greatest hero of Iran is undoubtedly Rostam, son of Zal, who lives for long centuries fighting for Iran under various Shahs (kings). Also worth mentioning are Esfandyar, the invulnerable prince, and Bahram Gur, with whom a whole lot of tales are associated (including Nizami's Seven Wise Princesses, which I introduced last year). The story also features some intriguing female characters, both slaves and royals, such as Gordiya the warrior maiden or Shirin, the poison-wielding matron of the royal harem.
And then there is Zal.
Zal and Rudabeh. It is a love story for the ages, between a white-haired prince who is raised by the colorful mythical bird Simurgh, and Rudabeh, the daughter of a nobleman descended from Zahhak, one of Iran's first kings who was turned into a dragon by his evil ways. Both outcasts in some way - Zal for his unusual coloring and Rudabeh for her bloodline - the two fall in love. Some say they are the origin of the Rapunzel tale, since Rudabeh offers to let Zal climb her braids to her tower (which Zal refuses because he is awesome and he brought a rope). They end up getting married and becoming the parents of Rostam (who is delivered by the world's first C-section, assisted by the Simurgh, who is better than any fairy godmother ever). The entire story, from start to finish, is amazing, and everyone should read it in its full glory.
Another tale that I really like is that of Esfandyar (I included it in my book about superpowers in traditional stories, since it features an invulnerable hero). It is the story of a struggle between father and son for the throne, in which the prince chooses honor over inheritance. He also goes through an epic journey fighting demons and monsters to rescue his sisters, and ends up being forced to fight Rostam to the death, something that neither hero wanted and both of them regret. It is one of the most eloquent parts of the epic.
There are two shorter stories that I like as well, one involving the invention of the game of chess and its arrival to Iran, and the other the story of how Kalila and Dimna was translated into Persian.
I also really love the miniatures and paintings that are used to traditionally illustrate manuscripts of the Shahnameh. They are full of bright colors, minute details, and life.