You've got 498 hit rating, the cap for melee (the vast majority of your damage) is 263. The big chunks that you could lose are on your weapon, shoulders and cape. Fortunately, there's plenty of good upgrades that you can get from the first four bosses of ICC10, which pretty much any group should be able to faceroll through with the 30% buff. My suggestion would be to pick up a Saronite Gargoyle Cloak from (heroic, if possible) gunship, then Ramaladni's Blade of Culling from Saurfang. In the mean time, pick up T10 shoulders with the frosties you get from running ICC, they're only 50. There are plenty of other options, but those are dead simple to get and you won't face much competition.
Aside from the hit cap bit, you're going to want a new helm with a +AGI/crit damage meta. T10 is a solid choice because it'd bring you up to 4pc along with the shoulders, but it'll take a while at 95 frosties. To activate the meta, just shove a Nightmare Tear somewhere where it'll get you a STR set bonus - your neckpiece would work fine for that. You'll also want new boots, check out the crafted 264 and 226 boots if you can't get any decent ones to drop.
I'd also like to add something on expertise. The gear I listed above brings you to 26 expertise, which is the "cap" for DPS. As people have noted, this is optional, but I *strongly* recommend it for beginning DKs. The reason it's optional is because Unholy's standard rotations have free GCDs, so you can afford a dodge or two - but if you're already dealing with dodges, you don't really have any room for error, and you'll be fucking up plenty while you learn raid DPSing in general and the fights in ICC. Keep the free GCDs for your own fuckups, and drop some expertise when you get awesome gear to replace it and know your shit.
Edit: One last note, all of this still applies if you decide to stay Blood, but the expertise bit becomes more important because Blood has fewer free GCDs.
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