Cataclysm shakes up players' ability to bring their allies back to life. More classes can battle ress, and hybrid classes can resurrect their whole group or raid with a single spell cast.
Originally part of the Guild Perk system, Blizzard decided to move Mass Resurrection to what they are calling «player perks». While in the original Cataclysm, every class had access to Mass Resurrection, now only classes that can heal have access to such spells. Adding more flavor to the mix, instead of giving them the default Mass Resurrection, each class has its unique flavorful mass ress spell.
Note that these are not learned by default as you log in, meaning you need to visit your class trainer to learn them if you can't find them in your spell book.
While only Druids could use battle resses in Wrath, now Warlocks and Death Knights can help raise their allies mid-combat. To compensate for these additions, however, Battle Resses now have strict rules in raids, with all battle resses while fighting a raid boss having charges and sharing cooldown. For 25m groups, you may only resurrect three allies while in combat, while for 10m groups, this number drops to one.
As the charges are shared, however, this means that a single person can do all resses, so you can have a 25m group with only a single Druid and this Druid can ress three people during a boss fight.
The battle ress spells in Cataclysm Classic are:
Warlock Soulstone Resurrection is unique as it allows the player to place a soulstone in someone allowing them to quickly ress after dying without requiring another player to react to their death. Note that this will still use a charge of the group's battle ress counter.