Dwarf and Troll Warlocks!
An exciting announcement was made by Ghostcrawler(source), citing that two new class/race combinations will be available in Cataclysm: Troll and Dwarf warlock.
This left many lore enthusiasts wondering: how?
Dwarf
Moira Bronzebeard is returning in Cataclysm as the leader of the Dark Iron dwarves. As warlocks are common amongst the Dark Iron people, it isn't insane to assume that the Dark Iron joining the new, united Ironforge will bring some Warlocks into their society. Warlocks were previously outlawed in Ironforge, and may still be. With the desperation and gloom in Cataclysm, perhaps the dwarves decide that they need their demonic friends more than they first thought.
Troll
Trolls have a long history of summoning dark entities and whispering hexes and curses. Their blood rituals are not a far cry from that of warlock rituals. With the presence of Magi in troll society, there is also inevitably a group of dark casters hidden amongst them. Trolls were, for a long time, the only race Magi who did not fall to the dark path. It looks like a decade of lore has changed that fact.