So here it is, my list of easy to obtain gear that will get you past that magical 689 defense rating so the big baddies in heroics and Naxx won't stomp you into oblivion. This is not best in class gear. It is gear a casual raider like me can pick up without a lot of effort.
Head: Helm of the Ley-Guardian, its a drop in the Oculus. 68 defense.
Neck: Blood Infused Pendent, quest reward. 26 defense.
Shoulder: Pauldrons of Reconnaissance, quest reward in Halls of Lightning. 46 defense.
Back: Cloak of Peaceful Resolutions, Wyrmrest rep reward honored. 43 defense.
Chest: Breastplate of the Solemn Council, Wyrmrest rep reward revered. 76 defense.
Wrist: Svala's Bloodied Shackles, drop in Utgarde Pinnacle. 27 defense.
Hands: Tempered Saronite Gauntlets, crafted. 66 defense.
Belt: Waistguard of the Risen Knight, trash drop in the Drak'theron, I found mine in the AH. 42 defense.
Pants: Daunting Legplates, crafted. 88 defense.
Feet: Sabatons of Draconic Vigor, Wyrmrest rep reward revered. 58 defense.
Ring1: Staunch Signet, quest reward in Oculus. 25 defense.
Ring2: Gal'darah's Signet, drop in Gun'drak. 36 defense.
Trinket: Seal of the Pantheon, drop in Halls of Lightning. 65 defense.
Gem: The gear above will have 1 red slot. Deadly Monarchs Topaz, crafted. 8 defense.
Enchant: Arcanum of the Stalwart Protector, Argent Crusade rep reward revered. 20 defense.
There you have it, 694 dfense rating. All you have to do is some quests while leveling, 6 dailies, and 5 dungeons and you can be uncritable and ready to tank heroics and Naxx.