Although I'm going to do a video presentation for each class, I thought I'd pass along some sage wisdom: It's always best to roll a "pure" class for your very first character.
Pure: Mage, Priest, Warrior, Rogue, Hunter, Warlock
Hybrid: Shaman, Paladin, Druid
The difference is that pure classes generally have one role, even though they don't always choose to fulfill that role (ie, priests are made to be great healers, but lots of us go shadow so we can kill things), and hybrids can fulfill several different roles (any hybrid can heal, two can tank, and all can damage). The pure classes are less complicated, and people generally know what to expect from you.