I've recently respecced, I'm tanking in blood mode only right now. I find it's the best mix for survivability/ threat and theres no1 except those OP pally tanks who can over aggro me in ICC. And if a DPS does over-aggro me, he/ she's stupid and deserves to die
If you're having trouble keeping aggro, make sure hit and expertise are high enough. It might even be worth it to switch out a stamina gem for hit/ expertise, preferrebly one that has hit/ stamina combined. And if you have rogues in your raid, they should use tricks of the trade to you. And it's good practice for raids to give the tank 2 seconds head start on the fight, to establish aggro. I usually kick off with a death and decay, but on fights like Festergut ( I run in, between his legs and turn him), I use Icy Touch, Blood plaque and take it from there.
Oh ye, do you have Rune Strike macro'd in on all your abilities?
#showtooltip <Original Spell>
/cast <Original Spell>
/cast Rune Strike
If rune strike is available, it will use your normal DPS ability and also hit with Rune Strike. Rune Strike is BIG threat builder for DK's. I've started using the macro recently, and it makes live a lot easier.
My main tanking weapon is the 2H axe which drops from Saurfang in ICC, I'm hoping we the guild can down him on herioc mode soon, I'd luv to have the 2H axe in ilvl 264

I find that axe to have sufficient DPS/ threat.
And ye, I'm also a jewelcrafter, I wanted those 51 stamina gems!!