The Alliance Vanguard is one of the main Alliance factions of WoTLK. The reputation is rather easy to raise since all it does is require you to -not- wear any faction specific tabard when running a level 80 instance. This is by far the best way to raise the reputation for Alliance Vanguard, I personally prefer either Halls of Stone (but I don't finish the instance, I just do the trash) or Halls of Lightning for grinding out reputation with the Alliance Vanguard. The best dailies for you to grind for the Alliance Vanguard faction are the dailies in Grizzly Hills and the one daily from Howling Fjord.
Howling Fjord Daily
You can get this daily from Bombardier Petrov in Howling Fjord. It requires you to hop on the Zeppelin that docks right near him and fly over the ocean to the north. When you're flying over the ocean you will unleash hell on the pirates from above.
This daily will give you 38 reputation with the Alliance Vanguard and 250 reputation with Valiance Expedition.