Average ilevels required for each set of dungeons
80-81: 226
82-85: 272
Heroic: 327
Zul Heroic: 346
New instance level breakdown
80-81: Blackrock Caverns (Blackrock Mountain), Throne of the Tides (Abyssal Depths)
82-84: The Stonecore (Deepholm), Vortex Pinnacle (Uldum)
84-85: Lost City of the Tol'vir (Uldum), Halls of Origination (Uldum), Grim Batol (Twilight Highlands)
85: Heroic Shadowfang Keep, Heroic Deadmines
85^1: Zul'Aman, Zul'Gurub
Where to go first
There are a number of excellent blue quality rewards available from quests in various zones, so I'm not going to get into them. Suffice to say that if you quest in Deepholm, Uldum, and Twilight Highlands, you'll run into some good starter pieces of at least level 318 ilevel. Don't pass up Deepholm upgrades even if they're green. That's the zone where the steepest upgrades come. You'll still need to upgrade from those, but they're an excellent starting point for obtaining said upgrades. Definitely do Crucible of Carnage in Twilight Highlands at 84. It's a major exp boost, plus you get a 333 blue bow!
Hunter reputation gear breakdown
Guardians of Hyjal: revered (346 blue necklace), exalted (359 epic boots)
Earthen Ring: honored (333 blue shoulders), revered (346 blue cloak), exalted (359 epic ring)
Therazane: honored (blue shoulder enchant), revered (346 blue ring), exalted (epic shoulder enchant)
Ramkahen: honored (333 blue belt), revered (helm enchant)
Wildhammer Clan/Dragonmaw Clan: revered (346 blue helm {alliance/horde})
Tol Barad (PvP area, but can do quests without PvPing): revered (346 blue dagger, 346 blue 1h axe, 346 blue polearm, 346 blue crossbow), exalted (359 epic trinket)
Some of these wonderful pieces, even from the starter zone factions, are 333 ilevel and you can wear them below level 85. 333 is the ilevel of the level 85 regular instance gear; heroic is 346. Do not discount the reputation vendor gear regardless of how soon you can get it.
There are dailies available for all factions except the Earthen Ring, so you'll probably want to prioritize that tabard first. You'll also get a ton of rep with them for questing in Deepholm and some of Vashj'ir and Twilight Highlands.
Available crafted items (these can be expensive)
Alchemy
BoP 359 epic trinket (you MUST be a 500 alchemist to craft)
Blacksmithing
346 blue polearm
346 blue 1h axe
346 blue dagger
316 blue polearm
316 blue 1h axe
316 blue dagger
Engineering
BoP 359 epic helm (you MUST be a 525 engineer to craft)
346 blue gun (slightly better stats than the bow below)
346 blue bow (hotfixed from epic to blue; same stats as before)
333 blue crossbow
333 blue gun
BoE 333 blue trinket (you MUST be a 475 engineer to use, but could have someone else craft)
Jewelcrafting
346 blue ring (hit)
346 blue ring (mastery)
346 blue neck (red socket)
346 blue neck (yellow socket)
333 blue fist weapon
317 green fist weapon
300 green ring; random stats (can proc as 325 blue version)
300 green necklace; random stats (can proc as 325 blue version)
Leatherworking
359 epic belt
359 epic chest
346 blue cloak
333 blue cloak
339 blue resilience set
mixed 308/333 blue and 295 green set; random stats
Decisions, decisions. 
But it's very nice. 
