There are a wide variety of different products that carry the World of Warcraft license.
Several different authors have written approved novels set within the World of Warcraft universe. The most notable of these writers is Richard A. Knaak, however books have also been written by Christie Golden, Aaron Rosenberg and Keith Decandido. Much like novels written for other fantasy universes like Star Wars, the novels follow the lore very closely, but do depart from it slightly.
WoW also made it's move in the graphic novel world, and a few Comic Books set within the World of Warcraft universe have been published. Most of the stories in the comic are now part of the lore, since event that happened in the game are often direct result of what happened in the comics - a chief example of this is the The Sunwell Trilogy, written by Richard Knaak, which leads directly to the creation of the Sunwell Instances which is the last raid instance of the Burning Crusade Expansion pack. In the same vein, the World of Warcraft Comic Book written by Walter Simonson is building up to the release of the Wrath of the Lich King expansion.
Upper Deck Entertainment has created a tradeable card game based around World of Warcraft. Many players have referred to it as an upgraded version of Magic:The Gathering. The most important aspect of the game for MMO players is the presence of loot cards that have scratch-off codes that can be redeemed for in-game loot.
UDE has also create a WoW miniatures game that is slated for release in late 2008.
Fantasy Flight Games sells a very intricate board game centered on World of Warcraft. The game is extremely elaborate and features hundreds of game pieces. In a similar vein, there are rules for playing Dungeons and Dragons in the WoW universe courtesy of a rules manual sold by White Wolf Publishing.
Epic Weapons is currently selling a replica sword of the Frostmourne. This weapon is the one Arthus / The Lich King wields himself.
DC Unlimited Has crafted a line of action figures modeled after the characters in World of Warcraft. Each series includes one larger-than-the rest deluxe figure.