I have read many poems so far, but personally this one is my favorite: Robert Frost's Stopping by Woods on a Snowy Evning:

Whose woods these are I think I know

His house is in the village though
He will not see me stopping here
To watch his woods fill up with snow.

My little horse must think it queer
To stop without a farmhouse near
Between the woods and the frozen lake
The darkest evening of the year.

He gives his harness bells a shake
To ask if there is some mistake.
The only other sound's the sweep
Of easy wind and downy flake.

The woods are lovely, dark and deep
But I have promises to keep
And miles to go before I sleep
And miles to go before I sleep.

"Stopping by Woods on a Snowy Evening" is an acknowledged masterpiece in short poetry, and one of Frost's best works. The rhyming scheme has that rhythmical beauty in it, (rhyming scheme: aaba, bbcb, ccdc, dddd), and it always gives me a sense of serenity- alone in the woods, the white snow falling all around... And I guess there are many ways to interpret this poem- I have read many comments on this-some people simply see a lone traveler taking a break with his horse; some people see a despaired old man wanting to finish his life but is stopped from doing so....
Apart from this one, I also love his other poem "The Road Not Taken"... It was actually once in our textbook, and I still can't forget it...