Deadly Boss Mods
Action bars of your choice - Paladins have a ton of spells, so action bar addon to expend (and to make it better looking and compact) vanilla bars.
Pally Power - Eases up buffing paladin buffs, easy to track missing ones, comes handy if more paladins have it (you'll see what other paladins are buffing, if they have PP).
Omen - Threat meter, you might want to use Hand of Salvation on some high threat DPS.
Paladin guides
ICC 25 (HC) guide. Might be partly outdated, but you get the idea of bosses' abilities and what to do.