Orc - Warrior, possibly warlock
Undead - Warlock or priests
Tauren - Shaman
Troll - Rogue or Hunter(More of a headhunter type of hunter, though.)
Blood Elf - Mage
Goblin - Rogue
Human - Paladin
Dwarf - Priest/Paladin
Night Elf - Druid
Gnome - Tricky. I'd go for a mage or similar.
Draenei - Priest or Paladin
Worgen - Another tricky one. The Worgen don't appear to have any classes that fully fit them. Possibly warrior.