In Destiny, if you pre-ordered, you get "early access to the Vanguard Armory." Where is this, and what benefits does it impart upon the player?
The Vanguard Armory is by the shipwright on the Tower. Go to the right when you first spawn and it's down that hallway.
The early access thing is a series of level 10 items that vary depending on your class. They're pretty good but by no means super amazing. When I hit level 10 I had only one gear piece that I bought there.
Note: You can talk to the robots hanging out in the Tower to see a map of the area. You can also use the Destiny Companion App to have a map and do other cool things like mess with your gear and read the grimoire cards.
[Disclaimer: I have not played Destiny. All information in this post is gained through secondary sources.]
According to the official website, the Vanguard Armory grants access to upgraded weapons. If you pre-ordered, you should find several vendors around the game that you can use Glimmer (the game's currency) to purchase. One of these vendors is located near the shipwright.
Although the official website only lists flavour texts for the "upgraded weapons" the Vanguard Armory gives, we can find more details about these weapons by looking them up on the Destiny wiki. For instance, one of the weapons the Armory gives is the Carte Blanche S.1, which is supposedly pretty powerful. 67 damage sounds like a lot I suppose, compared to the 36 of the standard rifles.
Note that Bungie's website says at the bottom:
Access to Vanguard Armory can also be attained through gameplay.
This probably means that the Vanguard Armory weapons can also be found if you do not preorder, but they will more difficult to find.