Plains

Benalish Marshal

White Knight

First strike (This creature deals combat damage before creatures without first strike.)
Protection from black (This creature can't be blocked, targeted, dealt damage, or enchanted by anything black.)

Mistveil Plains

({T}: Add {W}.)
Mistveil Plains enters tapped.
{W}, {T}: Put target card from your graveyard on the bottom of your library. Activate only if you control two or more white permanents.

Linden, the Steadfast Queen

Vigilance
Whenever a white creature you control attacks, you gain 1 life.

Daxos, Blessed by the Sun

Daxos's toughness is equal to your devotion to white. (Each {W} in the mana costs of permanents you control counts toward your devotion to white.)
Whenever another creature you control enters or dies, you gain 1 life.

Silverflame Ritual

Put a +1/+1 counter on each creature you control.
Adamant — If at least three white mana was spent to cast this spell, creatures you control gain vigilance until end of turn.

Anafenza, Kin-Tree Spirit

Whenever another nontoken creature you control enters, bolster 1. (Choose a creature with the least toughness among creatures you control and put a +1/+1 counter on it.)

Mirran Crusader

Double strike, protection from black and from green

Idyllic Grange

({T}: Add {W}.)
Idyllic Grange enters tapped unless you control three or more other Plains.
When Idyllic Grange enters untapped, put a +1/+1 counter on target creature you control.

Light from Within

Chroma — Each creature you control gets +1/+1 for each white mana symbol in its mana cost.

Honor of the Pure

Ardenvale Paladin

Adamant — If at least three white mana was spent to cast this spell, Ardenvale Paladin enters with a +1/+1 counter on it.

Fiendslayer Paladin

First strike (This creature deals combat damage before creatures without first strike.)
Lifelink (Damage dealt by this creature also causes you to gain that much life.)
Fiendslayer Paladin can't be the target of black or red spells your opponents control.