Everyone who attend raids should have the following addons. You agreed to install them in your application form
Voice and chat: Voice communication is key
Boss mod: Deadly Boss Mod or BigWigs
Raid mod: oRA2 or CT_RaidAssist
Threat meter: Omen or KTM
Raid and decurse frame (healers): A combination of Blizzard's default UI, CT_RaidAssist, Grid, Decursive as you like it. Basically, you need someway to see the whole raid (not just your group) so you can heal and decurse/cleanse/dispel people.
PallyPower (all paladins)
You should also have class specific mods that can improve your raid performance, eg DoTimer, necb, etc


Edwwin