Heart of Yavimaya

If Heart of Yavimaya would enter the battlefield, sacrifice a Forest instead. If you do, put Heart of Yavimaya onto the battlefield. If you don't, put it into its owner's graveyard.
{T}: Add {G}.
{T}: Target creature gets +1/+1 until end of turn.

Titania, Nature's Force

You may play Forests from your graveyard.
Whenever a Forest enters the battlefield under your control, create a 5/3 green Elemental creature token.
Whenever an Elemental you control dies, you may mill three cards.

Ramunap Excavator

Zuran Orb

Dryad of the Ilysian Grove

You may play an additional land on each of your turns.
Lands you control are every basic land type in addition to their other types.

Argoth, Sanctum of Nature

Argoth, Sanctum of Nature enters the battlefield tapped unless you control a legendary green creature.
{T}: Add {G}.
{2}{G}{G}, {T}: Create a 2/2 green Bear creature token, then mill three cards. Activate only as a sorcery.
(Melds with Titania, Voice of Gaea.)

Titania, Voice of Gaea

Reach
Whenever one or more land cards are put into your graveyard from anywhere, you gain 2 life.
At the beginning of your upkeep, if there are four or more land cards in your graveyard and you both own and control Titania, Voice of Gaea and a land named Argoth, Sanctum of Nature, exile them, then meld them into Titania, Gaea Incarnate.

Exploration

You may play an additional land on each of your turns.

Staff of Titania

Equipped creature gets +X/+X, where X is the number of Forests you control.
Whenever equipped creature attacks, create a 1/1 green Forest Dryad land creature token. (It's affected by summoning sickness.)
Equip {3}

Azusa, Lost but Seeking

You may play two additional lands on each of your turns.

Yavimaya, Cradle of Growth

Each land is a Forest in addition to its other land types.

Druid Class

(Gain the next level as a sorcery to add its ability.)
Landfall — Whenever a land enters the battlefield under your control, you gain 1 life.
{2}{G}: Level 2
You may play an additional land on each of your turns.
{4}{G}: Level 3
When this Class becomes level 3, target land you control becomes a creature with haste and "This creature's power and toughness are each equal to the number of lands you control." It's still a land.

Rites of Flourishing

At the beginning of each player's draw step, that player draws an additional card.
Each player may play an additional land on each of their turns.

Multani, Yavimaya's Avatar

Reach, trample
Multani, Yavimaya's Avatar gets +1/+1 for each land you control and each land card in your graveyard.
{1}{G}, Return two lands you control to their owner's hand: Return Multani from your graveyard to your hand.

Titania, Protector of Argoth

When Titania, Protector of Argoth enters the battlefield, return target land card from your graveyard to the battlefield.
Whenever a land you control is put into a graveyard from the battlefield, create a 5/3 green Elemental creature token.

Oracle of Mul Daya

You may play an additional land on each of your turns.
Play with the top card of your library revealed.
You may play lands from the top of your library.