Couplets are simply pairs of lines that rhyme. 

To My Dear and Loving Husband
Anne Bradstreet
IF ever two were one, then surely we.
If ever man were lov'd by wife, then thee.
If ever wife was happy in a man,
Compare with me, ye women, if you can.
I prize thy love more than whole Mines of gold
Or all the riches that the East doth hold.
My love is such that Rivers cannot quench,
Nor ought but love from thee give recompense.
Thy love is such I can no way repay.
The heavens reward thee manifold, I pray.
Then while we live, in love let's so persevere
That when we live no more, we may live ever.

Upon Prue, His Maid
Robert Herrick

In this little urn is laid
Prudence Baldwin, once my maid,
From whose happy spark here let
Spring the purple violet.   

Trees
Joyce Kilmer

I think that I shall never see
A poem lovely as a tree.

A tree whose hungry mouth is prest
Against the earth's sweet flowing breast;

A tree that looks at God all day,
And lifts her leafy arms to pray;

A tree that may in Summer wear
A nest of robins in her hair;

Upon whose bosom snow has lain;
Who intimately lives with rain.

Poems are made by fools like me,
But only God can make a tree.

from Romeo and Juliet
William Shakespeare

And, as he fell, did Romeo turn and fly.
This is the truth, or let Benvolio die