Mages can teleport there at level 71, and give portals there at 74. So that's one option. Similarly, you can get a Warlock to summon you, if they can find players around to help. Players also get quests to go there legitimately and get attuned to use the crystal that teleports you up and down at level 74, but who wants to wait that long?
Enter the Battleground summon. This is how I and almost everyone I know got to Dalaran the first time, and it goes like this:
- Find someone in Dalaran ("/who Dalaran" is helpful for this) and ask politely if they are willing to group with you and queue the group for a battleground.
- When you get into the battleground, /afk out (or play it through).
- Poof! You're in Dalaran.
This works at any level, for any character (although you do need to ensure the person queueing you is in the same battleground level bracket as you; thanks to Faeries Wear Boots for pointing this out). Once there you can set your hearthstone at any of several inns for quick return, and there is a flight point at Krasus' Landing - if you grab a flight point or two in Dragonblight for connections (Mo'aki Harbor being the easiest), you should then be able to fly to Dalaran from most flight points in Northrend.
Arthas awaits and so do your questions. Find the answers you've been looking for that will help you with your journey into Northrend and to level 80 with Wrath 101.