Some of this has already been said, but...
Rules for offering sacrifices to good deities and what you gain from doing so (reduced xp cost of manufacturing items or casting ritual spells, temporary higher caster level or free metamagicing, etc).
Oaths and vows. Effects of taking vows of chastity, monogomy (ei marriage), friendship, silence, and poverty, and the ritual act of making covenants.
New hinderances and feats with built in balancing effects (Merciful, Compassionate, Truthful, Honorable, Perservering, etc.)
Oath Feats - You gain power until you break the oath that is a prequisite for the feat and must atone (paying xp) to recover it.
Feats with names like:
'Come back with your shield or on it!'
and
'You can't do that to my friend!'
and
'Begone foul dwimmerlaik!'
Penitance and atonement. Pillgramage and advice for creating holy sites as well as the not so holy commerce (well I guess that depends on your point of view) that tends to grow up around them.
PrC's for Questing Knights and similar heroic themes.
Discussion of Paladin codes of honor based on the codes of honor of different cultures (Dark Age Europe, Feudal Japan, Chivalry, Rome, Confusius, etc.)
Epic and ritual spell casting with broad pervasive but subtle (well, not always) good effects... (The Land and the King are One!, etc.)
Examples of Arch-Celestials, proxies, heralds, and seneschals of deities.
Acquiring sainthood and divine rank.