Alliance Vanguard and Horde Expedition
Much like in Burning Crusade, the first faction you encounter in Wrath will be based on your side, and the quartermaster for either side will carry items that are mostly the same stat-wise.
If you're a fan of Phat Loot Phriday, chances are you may recall why this set of factions is a recommended grind for most Hunters. At revered and level 78, the Alliance will get access to the Sawed-Off Hand Cannon, while the Horde gets the Sin'dorei Recurve Bow. These weapons edge out the Crossbow of Relentless Strikes for DPS, so if you've been carrying it around since 70, here's a nice quick and dirty upgrade.
If you're a dual wielder, you might find that the level 78 Warsong Shanker, aka the Vanguard Soldier's Dagger, has a nice outlay of Hunter stats. Finally, if you PvP, you'll want to pick up the Arcanum of the Savage Gladiator. The arcanum is an exalted reward, while the daggers are revered.
This will likely be the second reputation you encounter in large numbers in Northrend. The Tuskarr are well worth the grind, especially since said grind isn't too difficult. A quick run through their quests in Howling Fjord alone is more than enough to gain honored.
At honored reputation, you'll find the pattern for the Dragonscale Ammo Pouch, as well as a good level 76 mail chest piece, the Cuttlefish Scale Breastplate. At Revered and level 78, the Whale-Stick Harpoon should prove a pretty solid weapon of choice for anyone who didn't get their hands on a badge or Arena weapon or better. Finally, even though it's not directly Hunter related, I'm going to encourage you to keep grinding to exalted. Not only do you get the best fishing pole outside of the Booty Bay fishing competition, you get a penguin pet. I firmly believe that you can never have enough pets.
The Oracles and the Frenzyheart
Next, we come to the Scryers and the Aldor of Wrath of the Lich King. In this case, I have to say that I believe the Oracles win out, both because they're not jerks and because they have the better rewards. Sorry Wolvar.
At revered, the level 78 Toothslice Helm not only looks pretty cool, it provides stats that make it pretty competitive with Gronnstalker, although it lacks the metagem slot. At exalted, the Oracle Talisman of Ablution provides not only a great amount of critical strike rating, but free mana on kill, perfect for chain pulling situations. Anything that keeps you out of Aspect of the Viper a little bit longer is probably a good thing, right? To top it all off, you can also buy the Mysterious Egg from the Oracles, which will eventually hatch into a variety of things, including one of three to four different vanity pets.
On the Wolvar side, there's honestly not much. Their only ranged weapon is thrown, and while it looks cool, it isn't a Hunter weapon. If you insist on grinding the Wolvar though, the Azure Scrappy Pants at honored aren't the worst you can do for a leg slot if you don't mind wearing leather, and at Exalted, you can grab a haste trinket that also gives a 10-second damage buff, which for my money isn't as good as the Oracle exalted trinket. They have a Disgusting Jar, but so far it doesn't seem to give out pets like the egg does, just Frenzyheart Brew, which is I suppose is okay if you like looking like a jerk.
The Argent Crusade is the reformed Argent Dawn, but there's more reasons to grind it than just the nostalgia factor. There's some pretty nice Hunter gear too.
At Honored and level 78, you'll be able to pick up the Cloak of Holy Extermination, which is essentially a greatly upgraded Dory's Embrace, shedding the critical strike rating and resilience for some nice juicy Agility. Chances are this cloak will be a good upgrade for you, at least for finishing the grind up to 80.
Revered gives you the opportunity for another ranged upgrade. The Zombie Sweeper Shotgun definitely blows all three of the ranged weapons we were discussing in the last section out of the water, with superior DPS, superior high end damage, and a good outlay of extra stats. You'll have to wait until level 80 to use it, though.
If you finish the exalted grind for the Crusade, you have one more level 80 reward coming your way: The Polished Regimental Hauberk. It has over double the agility of the Gronnstalker's Chestguard, and edges it out on most other stats too. Combine this with a very sizable portion of hit rating, and you'll likely want to consider this upgrade. If you don't mind the armor hit on yourself or your pet, the Boots of the Neverending Path are pretty solid for Hunter DPS too.
If you're a Beastmastery Hunter, grinding Kirin Tor reputation might give you pause, since many of their Hunter-friendly rewards have haste, which is dangerously close to useless for you. But other specs that need haste will probably be pretty happy with these.
At Honored, the level 78 Spaulders of Grounded Lightning offer a nice outlay of Hunter stats that any Hunter will want to consider. If you're a PvPer, there's a bit of resilience on there as well, so it's a good choice to fill out your gear until you can get a decent Arena rating. Dual wielders may want to take a look at the Lightblade Rivener, which provides agility, attack power, and haste. The other solid Hunter reward is at Exalted, where the Boots of the Twinkling Stars provide intellect, agility, attack power, and haste rating.
Knights of the Ebon Blade
Despite being mostly made up of plate-wearers, the Death Knight faction actually has some pretty useful rewards for other classes. If you're a Leatherworker, the Nerubian Reinforced Quiver pattern is obtainable at honored.
You'll definitely want to get at least revered with these guys, as the Arcanum of Torment is the PvE Hunter helm enchantment of choice. In addition, revered reputation also grants you access to the Spaulders of the Black Arrow, a solid set of DPS shoulders. For weapons, the Runeblade of Demonstrable Power is nice for Marksmanship and Survival Hunters, with a solid balance of agility, attack power, haste rating, and critical strike rating that blow old high-end favorites like The Blade of Harbingers out of the water. Dual wielders may also find that the Reaper of Dark Souls is a good upgrade for them. All of these rewards are, of course, level 80.
The Wyrmrest Accord
The Dragons may still be mad at us for that whole Dragonstalker armor deal, because their Hunter rewards are few and far between. Dual wielders may find the Fang of Truth to their liking at honored reputation. If you don't mind wearing leather, you can also grind to exalted to get the Dragonfriend Bracers, which have a nice amount of attack power, critical strike rating, and agility. And face it, you'll probably be grinding to exalted eventually for the dragon mount.
The Sons of Hodir
These are another faction you'll definitely want to grind for, since they provide shoulder enchantments for your end-game. At Honored, you can get the Lesser Inscription of the Axe, and at exalted, the Greater Inscription of the Axe.
In other rewards, the Giant Ring Belt at Honored has some solid Hunter stats, while at revered, you can get some good solid dual-wielder Hunter weapons in the Broken Stalactite and the Stalactite Chopper. And before you ask, no, these mammoth mounts do not come with vendors, sorry.
As you can see, you can find an excuse to grind just about any reputation in Wrath you want. In the end, it's probably up to you to decide what's most important to you. Me, if I was pressed for time, I'd probably focus on the Argent Crusade, the Oracles, and the Kalu'ak. All three have rewards both useful and fun that I really want to get my hands on. But look over the rewards, take as much time as you need, and then choose. But choose quickly. After all, the next expansion may only be a couple of years away.