Color Me A Rhyme  by Jane Yolen. This poem introduces new words for colors in nature such as alabaster, ebony, saffron, vermilion, mahogany, azure, and verdure. (Try writing a poem as a follow up activity.)

Creatures of Earth, Sea, and Sky by Georgia Heard. Both delicate and forceful, reverential.

Earth Dance by Joann Ryder . A poetic, environmental book.

The Earth Is Painted Green by Barbara Brenner.

The Great Smoky Mountain Salamander Ball by Lisa Horstman. A funny story in rhyme that teaches respect and responsibility.

Insectlopedia by Douglas Florian. Clever rhymes, a great read aloud.

My Mama Had A Dancing Heart by Libba Moore Gray. A good book for choral reading. Lyrical language celebrates the seasons.

My Many Colored Days by Dr. Seuss. A book about feeling and moods illustrated after Seuss's death.

Old Elm Speaks - Tree Poems and The Great Frog Race and Other Poems both by Kristine O'Connell George. Non-rhyming poetry that children absorb, and use to inspire their writing. Here's a poem from Old Elm Speaks:

Old Elm Speaks

It is as I told you, Young Sapling.
It will take
autumns of patience
before you snag
your
first
moon

Ordinary Things by Ralph Fletcher. Strong poetry about everyday things. Example:

wind

the calendar says it's early spring
but the wind pretends not to know

it reaches with bone-cold fingers
inside my coat to rattle my ribs

it swoops down into my mouth
stuns my tongue, steals my voice

it whispers secrets past my ear a
blur of words too fast too low

Poems Have Roots by Lilian Moore (and earlier work by Ms. Moore. Sam's Place - Poems From the Country is out of print but worth finding). Example:

GREEN

Ducklings
look around.

there's treegreen
filling the sky

and there's grassgreen
running
up the hill,
steeply.

The shadowgreen is
pine woods,
dark
old.

The yellowgreen is
young leaf
unfolding,
new
as you.

Breathe green
deeply.

Silver Seeds by Paul Paolilli. Introduce children to acrostics, such as:

FOG

Folds and folds
Of spun sugar, like a soft
Gray blanket over the land

Spectacular Science - A Book of Poems selected by Lee Bennett Hopkins.  About science, questions, and wonder.

The Spider and the Fly by Mary Howitt, illustrations by Tony DiTerlizzi . A poem about spiders with a lesson. 

The Sky Is Full of Song and Moments: Poems About the Seasons by Lee Bennett Hopkins.

Something New Begins by Lillian Mooore.

Water Music by Jane Yolen. Photos, shaped poems, and many other forms of poems about water.

When the Frost in on the Pumpkin by James Whitcomb Riley. A classic ode to autumn in dialect.

Wings on the Wind - Bird Poems by Kate Kiesler. A collection of poems celebrating birds.