Taunka: A race of buffalo men, the Taunka are relatives of the Taurens, but are at odds with the passive Tauren philosophy regarding how they deal with the land. Where the Tauren live together with Nature, the Taunka bully the land around them into subservience. When a storm threatens their people, they beat the air elementals into submission until the threat passes. They are very much bullies of nature (no pun intended.)
Tuskarr: Originally a developer's joke when they were placed into earlier Warcraft games, the Tuskarr are now a very real, very powerful race of noble nomadic fisherman.
Iron Dwarves: We do not know much about this race, other than they are tied to Ulduar, the dwarven creation myth, and are one of the few evil races of dwarves in Azeroth. They have a large role in one of the major plot lines to be told in WotLK.
Vrykul: Imagine 8-foot-tall vampiric vikings with a lust for blood and penchant for evil. The Vrykul are one of the first races you encounter as you step off the boat in Howling Fjord, and they are definitely not happy to have us invading their territory.
Nerubians: We are not told much about what might be left of Azjol-Nerub, but adventurers in Northrend will be investigating the former Nerubian homeland, but there are hints that at least some part of this ancient civilization remains.
Grizzlemaw Furbolgs: Grizzley Hills is homeland to this mysterious race of Furbolgs, although it is unclear if this is the original race of furbolgs, or another off-shoot.
No doubt there will be more people and creatures as we explore Northrend; these are just the few that were highlighted during the convention. As we hear more information about the populace of the northern continent we'll be sure to pass it along.