Work on items over level 70

Might as well use any you have left over for those while you level until you come across a replacement weapon. Don't even think about using Mana Oils or Wizard Oils (or stones) as they will not work on items over level 70. Pro tip: Chances are, you'll be using your present weapons for a while.
Obsidian Sanctum
This is the first entry level Onyxia style boss you'll encounter. Sartharion is surrounded by 3 mini-boss dragons. Think of it as a modified Zul'Aman instance challenge. You can set the difficulty of the encounter by sparing any number of dragons. Leaving all 3 up when you engage Sartharion results in more items (and better quality). The Sanctum is also located in Dragonblight below Wyrmrest Temple.
The Eye of Eternity
Malygos makes the Eye of Eternity his domain. This is the only raid instance you will find in The Nexus. Before you can summon Malygos, you need to have the Heroic Key to the Focusing Iris (or its 10 man counterpart, the Key to the Focusing Iris). It'll be the first instance where you get to engage the boss on flying mounts!
Naxxramas
It once hovered over the Eastern Plaguelands. Now you can find this entry level instance in Dragonblight to the east. Players that experienced the old version of Naxx will notice many similarities in this latest rendition. Many of the bosses have returned (with the exception of a particular Knight from the 4 Horsemen).