Some chatter about this DK tank build caught my eye: 45/26/0
It's a build designed for 5 or 10-man content. It brings two major buffs to the raid: 10% Attack Power and 20% Melee Haste. Both are very important buffs that may not be covered. It also has the full 20% melee slow debuff. Raid buffs are very important, and sometimes it's hard to get full coverage in a smaller group. It also brings a Hysteria to further boost melee damage.
Defensively, it includes Will of the Necropolis and Vampiric Blood. It doesn't have 5% dodge, but it does have 3% additional melee miss chance. That should be good enough for lower content.
It's a two-handed weapon build. It plays like a regular Blood build, only you use Obliterate instead of Death Strike, and you have to refresh diseases more often. It probably won't do as much threat as a pure Frost or pure Blood build would do.
It's a pretty interesting hybrid Blood/Frost build. In some ways, it makes the DK an enhancement shaman replacement, as you bring the buffs an enhancement shaman usually would provide (Strength of Earth Totem, Unleashed Rage, and Windfury Totem). Of course, if your group already has an enhancement shaman, there are probably better tank builds.