Omnath, Locus of Mana

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

Glissa Sunseeker

First strike
{T}: Destroy target artifact if its mana value is equal to the amount of unspent mana you have.

Forest

Mana Reflection

If you tap a permanent for mana, it produces twice as much of that mana instead.

Cryptolith Rite

Creatures you control have "{T}: Add one mana of any color."

Upwelling

Players don't lose unspent mana as steps and phases end.

Horizon Stone

If you would lose unspent mana, that mana becomes colorless instead.

Birds of Paradise

Caged Sun

As Caged Sun enters, choose a color.
Creatures you control of the chosen color get +1/+1.
Whenever a land's ability causes you to add one or more mana of the chosen color, add one additional mana of that color.

Doubling Cube

{3}, {T}: Double the amount of each type of unspent mana you have.

Mana Geode

When Mana Geode enters, scry 1.
{T}: Add one mana of any color.

Gauntlet of Power

As Gauntlet of Power enters, choose a color.
Creatures of the chosen color get +1/+1.
Whenever a basic land is tapped for mana of the chosen color, its controller adds an additional one mana of that color.

Astral Cornucopia

Astral Cornucopia enters with X charge counters on it.
{T}: Choose a color. Add one mana of that color for each charge counter on Astral Cornucopia.

Arcane Signet

{T}: Add one mana of any color in your commander's color identity.

Ilysian Caryatid

{T}: Add one mana of any color. If you control a creature with power 4 or greater, add two mana of any one color instead.