Answer:
If you're talking about the storyline characters I can't help you, as there are way too many to list. Try going on WoWWiki for detailed information on the plot and the characters that make up the World of Warcraft.
If you mean the type of characters you can make though, you have many combinations which are based mostly on your class and profession. I'll enumerate these:
Classes: Druid, Hunter, Mage, Paladin, Priest, Rogue, Shaman, Warlock and Warrior.
Professions: Blacksmithing, Engineering, Alchemy, Leatherworking, Tailoring, Jewelcrafting, Herbalism, Mining, Skinning, and Enchanting.
Note that each of the classes has three different branches he/she can specialize in, which are called "talent trees". It's complex to explain it this way to a person who's never played it