Omnath, Locus of Mana

You don't lose unspent green mana as steps and phases end.
Omnath gets +1/+1 for each unspent green mana you have.

Wild Growth

Enchant land
Whenever enchanted land is tapped for mana, its controller adds an additional {G}.

Arbor Elf

Elvish Mystic

Llanowar Elves

Vernal Bloom

Whenever a Forest is tapped for mana, its controller adds an additional {G}.

Birds of Paradise

Zendikar Resurgent

Whenever you tap a land for mana, add one mana of any type that land produced. (The types of mana are white, blue, black, red, green, and colorless.)
Whenever you cast a creature spell, draw a card.

Utopia Sprawl

Enchant Forest
As this Aura enters, choose a color.
Whenever enchanted Forest is tapped for mana, its controller adds an additional one mana of the chosen color.

Fyndhorn Elves

Burgeoning

Whenever an opponent plays a land, you may put a land card from your hand onto the battlefield.