Warning: This post contains spoilers for Icecrown Citadel.
Blizzard did PTR testing for Valithria Dreamwalker today. It looks like a hilariously awesome fight. Here is MMO-Champion's post discussing her.
Valithria is a friendly green dragon captured by the Scourge. She starts at 50% and must be healed to 100%. Meanwhile, waves of Scourge are attacking, and must be held off by the rest of the raid.
This sounds like quite an interesting fight, and I am greatly looking forward to it.
It will be interesting to see what classes evolve to be the chosen healers for it. The easy assumption is to say Paladins, but there is a Druid build which can pump out more single-target HPS (single-target only, Beacon doesn't work with Valithria). Even Priests and Shamans can do large amounts of single-target HPS if they put their minds to it.