My honest answer is probably The Raven, but I'll post something less well known.

Gray Room

by Wallace Stevens

Although you sit in a room that is gray,

Except for the silver

Of the straw-paper,

And pick

At your pale white gown;

Or lift one of the green beads

Of your necklace,

To let it fall;

Or gaze at your green fan

Printed with the red branches of a red willow;

Or, with one finger,

Move the leaf in the bowl--

The leaf that has fallen from the branches of the forsythia

Beside you...

What is all this?

I know how furiously your heart is beating.