Frost mage specced into Enduring Winter
Destruction warlock specced into Soul Leech
Retribution paladin specced into Communion
Shadow priest specced into Vampiric Touch.
Resto druid with Revitalize.
It's my opinion that Blizzard has absolutely balanced heroic content around having this buff, which is why it's been given to more classes. This buff can make the difference between a straightforward clear and a difficult slog.