At Blizzcon, Blizzard revealed the fourth class in Diablo IV: the Rogue.
The Rogue is your typical Dexterity-based character. Interestingly enough, it covers both ranged and melee, making it unlikely we'll see another class focused on one type. I think it looks pretty good, with a nice back-to-basics vibe, rather than something exotic.
The classes previously revealed are Barbarian, Druid and Wizard. So naturally enough, everyone is speculating about the fifth class. The two big archetypes missing are the heavy plate wearer with a shield, or a summoner class.
I'm hoping for the Paladin, or a similar class like Crusader or Templar. Alternatively, I'd like something new. Though not a Death Knight variant. So far Blizzard is playing it really safe with Diablo IV, and I would like to see at least a little bit of innovation.