Well, we have the video of 4x Blood DK's, in PvP gear...
Doing a heroic, with I believe a Priest (also in PvP gear).
Basically a 4x DK + 1x Heals team.

The other gimmick/non-traditional teams that have reported success are the double-healer teams.
The equivalent of 2x Holy Paladin (Beacon a DPS, and Protector of the Innocent heal themselves) who can double heal through burst or alternate heals for longevity.
The other combo mentioned a lot was double Resto Shammies, with 2x Riptide + Earth Shield on the tank.

If you want a more traditional team...
Nothing is going to stop you from running...
Tank: Blood DK
Heals: Resto Druid
DPS: 3x Anything.