The Wheel of Time (Series)
Robert Jordan's The Wheel of Time is perhaps one of the richest and most detailed (and therefore, most realistic) fantasy worlds ever created. This brief summary obviously cannot do justice to a series which is eleven books and counting (with most books weighing in at over seven hundred pages), but this is the attempt at giving a spoiler free idea of the basics.
The source of all magic is called the One Power. It is divided into saidar, which only women can use, and saidin, which only men can use. The story takes place in the Third Age, an age where saidin (the male half of the Source) has been tainted by the Dark One, so any man wielding the Power slowly goes insane and eventually dies of a wasting disease (sometimes lashing out with their magical abilities and harming others in fit of insanity).
The Aes Sedai are a group of powerful women (long ago, men were members as well, but that ended when saidin became tainted) who use the One Power, supposedly in the name of public good. The Aes Sedai are aided by their Warders, strong men who choose to share a psychic bond with the particular woman to whom they are bonded. Although the Aes Sedai could use their magical abilities to force the Warders to do whatever they wish, each Warder acts as a trusted co-worker and loyal friend to his particular Sedai. Additionally, the Aes Sedai divide themselves into seven different Ajahs. The Aes Sedai of the Blue Ajah concern themselves with their individual causes and interests; Browns are devoted to the acquisition and preservation of knowledge; Grays mediate disputes; the Green Ajah holds itself ready for battle; Reds focus on preserving the Tower and preventing another breaking; the White Ajah is devoted to logic; and the Yellow Ajah is devoted to Healing. One of the most powerful male channelers from approximately three thousand years ago named Lews Therin Telamon (also known as The Dragon or the Kinslayer) is prophesied to be re-born so that he can sacrifice himself in order to save everyone from the return of Shai'tan (the Dark One) at Tarmon Gai'don (the Last Battle). Our young hero, Rand al'Thor, would appear to be the Dragon Reborn. As he and his childhood friends from the small town of Two Rivers explore the world, they gradually begin effecting enormous changes to the status quo. There's a lot more than that to it, of course. Read the books if you want to discover the rest!