The choices for legs and feet slots are obvious, since we've started on the respective sets last week.
Legs: Spellstrike Pants
Feet: Frozen Shadoweave Boots
Both these items will see you through much of tier 4 content - Karazhan and even early Tempest Keep and Serpentshrine Cavern. Their only weakness is the lack of basic stats, particularly Stamina. However, at this level of content, warlocks should have no survivability issues, if you are prudent with threat and positioning during encounters. That said, there are some alternatives that provide more durability while sacrificing a little raw DPS performance.
For the legs slot, Battlecast Pants are the high-Stamina crafted alternative to Spellstrike. An easier option to get is Dreadweave Leggings though, if you're headed this route. If you're running Black Morass regularly, make sure you roll for Khadgar's Kilt of Abjuration.
Some non-tailoring alternatives to the FSW Boots are Shattrath Jumpers from questing and Vindicator's Dreadweave Stalkers from PvP. Assuming that you have access to the heroic instances, Boots of Blasphemy, from the final boss of Slave Pens, is something worth looking out for.
Back: Sergeant's Heavy Cloak
A common theme in this guide is the getting great PvE gear through PvP. The back slot is a prime example of this. For less than 8,000 honor and 20 marks from Arathi Basin, you get this respectable cloak that does well in both PvP and PvE. For sheer spell power, Cloak of the Black Void is a crafted alternative that offers an unbeatable 35 spell damage, but pretty much nothing else. The Cloak of Woven Energy is also a good item to quest for.
Wrist: Vindicator's Dreadweave Cuffs
Another PvP recommendation here, because it offers the best bang for the effort. If you can gather up a group for Shadow Labyrinth, Shattrath Wraps is probably the easier option as a quest reward. Bracers of Havok is a nice crafted option for this slot, if you have the pattern or know someone who has it.
Hands: Tempest's Touch
Grab a team and rescue Thrall in Old Hillsbrad Foothills and get this as a quest reward. If you have trouble assembling a team, Gloves of the High Magus may be an easier option. If you want to try your luck, Jaedenfire Gloves of Annihilation and Energis Armwraps are good drops out of Shadow Labyrinth and Botanica respectively.
Rings: Vindicator's Band of Dominance and Evoker's Mark of the Redemption
If you are aligned with the Scryers, Manastorm Band and Seer's Signet are also available to you, the latter requiring some dedicated grinding to Exalted reputation. Veteran's Band of Dominance remains a good ring, and is a cheaper - in terms of honor - alternative to the Vindicator version. Note that you can equip both versions of the PvP ring.
Waist: Belt of Blasting
This top-end belt is now accessible to pre-raid toons since Nether Vortices have become tradeable. The absence of Stamina makes this belt less than ideal for PvP, but the DPS numbers and two gem slots are simply unbeatable till much later in the game. Notable placeholders - while you farm up the gold and mats for this - include Akama's Sash and A'dal's Gift, both of which are rewards from quests that require some form of group work. You can also consider going the PvP way with Vindicator's or Veteran's Dreadweave Belt.
Trinkets: Ancient Crystal Talisman and Vengeance of the Illidari
You should already have obtained these two items while you were leveling. Glowing Crystal Talisman is the Alliance version of Ancient Crystal Talisman. A notable trinket to get is Starkiller's Bauble, which should help you with achieving the hit cap. In a similar vein, Scryer's Bloodgem is a must-get for Scryer warlocks when you hit Revered with them. As soon as you start accumulating badges, you should be working towards Icon of the Silver Crescent. Quagmirran's Eye and Timbal's Focusing Crystal are important drops out of heroic Slave Pens and Magisters' Terrace respectively.
Wand: Gladiator's Touch of Defeat
Keeping in mind that Arena Season 4 is just around the corner, the Merciless version of this wand will soon be purchasable with honor - so you may want to pony up for that instead. Many of the best pre-raid and pre-heroic wands in the game are unfortunately instance drops: Wand of the Netherwing is a good example, out of Shadow Labyrinth. Scryer warlocks can choose to quest for Wand of the Seer. If you are running heroic Underbog, don't let The Black Stalk slip you by. Work towards getting Carved Witch Doctor's Stick when you start accumulating badges.
Mainhand/ Offhand: Merciless Gladiator's War Staff
This staff will also be purchasable with honor when Season 4 lands, and it is a worthwhile investment of time and effort that will see you well past tier 4 content. If you don't want to PvP your brains out for this (it will cost at least 27,000 honor), you can simply buy The Bringer of Death from your neighborhood AH. For those of you who prefer the dagger or sword-offhand combo, The Saga of Terokk and Summoner's Blade are examples that can be quested for, with some help. If you're running instances, make sure you roll for these items:
With this I'll conclude this gear guide by saying that we are on a tail end of an expansion and you may have trouble finding people who would run non-heroic instances. On the flipside, you may find help from people who are actually over-geared for heroics and don't mind having your toon tag along. Gear is important in WoW but it is merely a "key" to open up more experiences at endgame. Gear up, have fun, but don't QQ when your "hard-earned" epics are replaced by greens in a few months' time.
V'Ming is still dreaming of prancing up Mount Hyjal with his 24 friends.