I recently turned my attention back to one of my 'locks that I had pretty much stopped playing after Trial of the (Grand) Crusader. This means that his gear isn't bad by any means but that there are quite a few upgrades I can get for him without even having to get him raiding again. Pretty much all of these items come from spending Emblems of Frost.
Emblems of Frost can be collected a number of ways, the easiest being the random heroic. Completing a random Lich King heroic dungeon (using the dungeon finder tool -- /LFD) for the first time each day will earn you two Emblems of Frost, so that's 14 each week. Do note that the random element of this tool is the dungeon; feel free to form your own party before using it. You can also do the weekly raid quest for another 5 emblems. Toravon the Ice Watcher is holding a couple more for you, so if you can kill him on 10- and 25-man modes, then you can bag another four from him. To collect any more in a week you need to raid Icecrown Citadel, where if you clear it and do the ICC quest, you can get up to 60 more. After the break, we'll see what we can spend them on.
The most obvious gear to blow your hard-earned emblems on is the tier 10 set. The basic set (the one you can buy with emblems) is item level 251, which is actually lower than the heroic tier 9 set. If you do compare them, most of the stats are lower, especially spirit, but there's a big gain in haste for the tier 10. It also looks like warlock gear and not like something you stole from a mage. Anyone not wearing the best tier 9 gear set is probably going to find a nice upgrade in tier 10.
Another advantage with the tier 10 items is that you don't waste the emblems should you wish to upgrade. With tier 9, you had to save up a load of emblems and then decide whether to buy the lowest quality items or hold out until you had a Trophy and go for the better ones. With tier 10, you only spend emblems on the lowest item level gear and then use the item and the boss tokens to upgrade. Meteor Chaser's Raiment is a better chest item than the basic tier 10 robe. However, you do need to factor in how many set bonuses you are aiming for and whether you expect to be able to upgrade your set pieces to the ilvl264 or even 277 versions. The Gloves of False Gestures are in pretty much the same boat, but I feel they are far more on a par with the Dark Coven Gloves and so less reason to not use the set item.
So what else do our friendly Emblem of Frost Quartermasters have for us? Well, there's Volde's Cloak of the Night Sky, which is rather nice. Though it just struck me that it's the same model as the Death Knight reward from the quest Tonight We Dine In Havenshire. Well, I can live with that; it goes pretty well with the Dark Coven stuff.
The Belt of Omission is almost best in slot if you need the hit rating; otherwise, the Circle of Ossus is also a very nice purchase. They have very few items in the game that are better than them, but do bear in mind that one of them drops off the very first boss in Icecrown Citadel. The Crushing Coldwraith Belt is almost identical to the Circle of Ossus (swapping some spirit for crit), so if you are killing any bosses in 25-man ICC then this may come your way.
If your trinket slots are needing some ilvl264 love then there is an option for you. Maghia's Misguided Quill is a very powerful item that is one of the best in the game, but (yes, it's a big but) it's only good if you need all the hit rating it offers. One hundred fifty-two hit in one item is going to make it awkward to upgrade later without spending some time over the cap or having upgrades sit in your bags until you can find some more with more hit rating. If you are at the hit cap without a trinket then this one is essentially useless and you're better off with the Abyssal Rune from normal Trial of the Champion.
That's pretty much it for the Emblem of Frost vendors. If you are overflowing with Emblems then you could spend them on Primordial Saronite to craft either the Deathfrost Boots or the Leggings of Woven Death. The boots are great and well worth crafting if you can afford them, but it's probably better to grind for the cash to buy the Primordial Saronite rather than blow your Emblems on them. The legs are good but not worth getting over the tier item, so they are worth it if you have gold to burn but are short on emblems -- but otherwise, go for the Dark Coven Leggings.
As always, gear selection is a very personal thing. I've tried to give an overview of the options you have from Emblems of Frost, but don't get too focused on these items. I strongly suggest you use SimulationCraft to find out what stats you will gain the most from increasing and choose upgrades based on that. Blood Pact covered the basics on doing this a few weeks back, if you need a hand with it.
Blood Pact is a weekly column detailing DoTs, demons and all the dastardly deeds done by warlocks. If you're curious about what's new with 'locks since the last patch, check out WoW.com's guide to patch 3.3 or find out what's upcoming in Cataclysm from the BlizzCon 2009: Class Discussion Panel.