If you're looking to try out some Northrend dungeons, Howling Fjord and Borean Tundra both play host to a few of Northrend's earlier dungeons. Summoning stones at Northrend dungeons and raids, as well as the warlock spell 'Ritual of Summoning,' can also be used to summon you, although they require two and three people, respectively. There are a couple other ways to get to Howling Fjord and Borean Tundra.
Like the Alliance hubs in these zones, Vengeance Landing and Warsong Hold both feature profession trainers, flight masters, vendors and inns, as well as starting quests for Horde players. These zeppelins are distinct from others, featuring bladed battering rams and a shark-like paint job on the balloon. Horde players can make the trip to Howling Fjord and Borean Tundra via two specialized zeppelins. Both Valgarde and Valiance Keep feature a full complement of profession, flight masters, vendors and inns, as well as the first quests available to Alliance players in their respective zones.
These ships can easily be distinguished by their paddle wheels and eagle-like figureheads. Alliance players can reach Howling Fjord and Borean Tundra by riding one of the two Alliance icebreaker ships making their way to Northrend.
Generally, getting to these zones requires a ride on an Alliance icebreaker ship or a Horde zeppelin, although there are a couple of alternatives.