Shadowflame Hood Another tier piece and something I'd actually spend my valor points on. Confers a lot of haste and mastery. [EDIT: As correctly pointed out by themann1086, this item isn't actually available for valor points. You'll need a token drop from raids, so you won't be getting this anytime soon. It's pretty, though, so hey, enjoy the link!]
Honorable mentions: Cowl of Pleasant Gloom and Helm of the Typhonic Beast Both of these iLevel 346 items have identical stats including 162 hit rating. The only difference is that the Cowl of Pleasant Gloom has a blue socket and grants crit, while the Helm of the Typhonic Beast has a yellow socket and grants mastery. Stat-wise, the helm edges the cowl, but the Cowl of Pleasant Gloom looks completely badass, so it's a draw. You can buy the Cowl of Pleasant Gloom for justice points while the Helm of the Typhonic Beast drops off Setesh in heroic Halls of Origination.
Breeches of Mended Nightmares or Flame-Ascended Pantaloons If you're a tailor, congratulations, you can probably make either of these yourself. You can buy the BoP patterns from vendors in Twilight Highlands for one Dreamcloth. It will just take a lot of farming (or gold, if you're inclined to buy it at the auction house) to gather the materials, but I'm a fan of things you can technically rush. You can also have a tailor make it for you as these are BoE.
Shadowflame Leggings Here's another tier piece that can drop off Argaloth in Baradin Hold. So keep that in mind while considering what to spend your valor points on.
Honorable mentions: Pensive Legwraps and Legwraps of Astral Rain Both items are again nearly identical, but the former confers haste while the latter confers mastery. Pensive Legwraps can be bought for justice points at your respective quartermasters, while the Legwraps of Astral Rain drop off heroic Isiset in heroic Halls of Origination.
Shadowflame Mantle If you're going to spend your valor points, spend them on the shoulder piece first. They have a unique model, confer a tier bonus, and this piece in particular confers loads of hit. [EDIT: Similar to the head tier piece above, themann1086 correctly pointed out that this item isn't actually available for valor points. You'll need a token drop from raids, so enjoy the blues below!]
Honorable mentions: Mantle of the Eastern Lords, Mantle of Master Cho, and Meadow Mantle Out of the three nearly identical iLevel 346 items, the Mantle of the Eastern Lords from Lord Godfrey in heroic Shadowfang Keep edges out the other two because it has hit. If not that, you can get crit from the Mantle of Master Cho from Siamat in the heroic Lost City of Tol'vir or spend for mastery with Meadow Mantle, available for justice points.
Dreamless Belt This is about as good as it gets before raiding, and I highly recommend that you craft it or have someone tailor it for you. As with the pants, the pattern for this belt can be bought for Dreamcloth in the Twilight Highlands. Note that Dreamcloth has a seven-day cooldown, which will make it extremely expensive especially in the early goings of the expansion. But I'd imagine you'd have an easier time sourcing it than getting Belt of Arcane Storms to drop from Maloriak in Blackwing Descent.
Honorable mention: Stratosphere Belt Out of the several rare options you have for your waist, the Stratosphere Belt is the only one with hit. It drops from Grand Vizier Ertan in heroic Vortex Pinnacle. There's also the justice points-bought Incense Infused Cumberbund (misspelled!) and Beauty's Silken Ribbon from Beauty in Blackrock Caverns.
Bracers of the Dark Pool The good news is that the best preraiding bracers you can get are BoE. The bad news is that they're a zone drop from a raid, which means that they're highly unlikely to find their way to the auction house. Your best shot at these is to keep raiding The Bastion of Twilight in the hopes of winning the roll against a crappy mage.
Honorable mention: Sand Silk Wristband and Armbands of the Exiled Architects Fortunately, the blues that drop off heroics aren't too shabby, either. In particular, the Sand Silk Wristband that drops off Augh in the heroic Lost City of Tol'vir has excellent hit and you should probably aim for this, as it's far easier to obtain. The Armbands of the Exiled Architects (the name sounds like it should drop from the Lost City, but who knows how loot gets around) are a solid second choice, dropping from Vanessa VanCleef in heroic Deadmines.
Stump of Time This is why it's important that you participate in Tol Barad, even for the daily questing. Complete the daily quests every day diligently and pick this up from your respective quartermaster. It's 321 hit rating with a chance to proc a spellpower bonus. This is probably the best raiding trinket you can get this early on in the expansion.
Soul Casket Because there's a dearth of really good trinkets within easy reach, I'm not actually averse to the idea of using valor tokens to get this. It's a hefty mastery bonus and an on-use ability that means a spellpower bonus with a 16.6 percent uptime if you're conscientious.
Darkmoon Card: Volcano I'm a big fan of Darkmoon Cards, and Volcano seems to be the best one for warlocks right now. I'm not sure about the proc rate, but this is identical with Soul Casket in terms of mastery. It also works better if you don't want to use activated abilities as its a proc on any damage spell. Destruction warlocks will probably enjoy this a lot.
Honorable mentions: Anhuur's Hymnal and Gale of Shadows Because of sheer hit, Anhuur's Hymnal from Temple Guardian Anhuur in heroic Halls of Origination is an excellent choice for a trinket in lieu of the epic ones listed above. And since all warlocks of every spec use DoTs, the Gale of Shadows from Erudax in heroic Grim Batol is a great choice for the second slot, as well. It also adds haste, which ranks pretty high on the warlock stat weight list.