My absolute favourite poem by an Irishman is The Ballad of Reading Gaol by Oscar Wilde. Much too long to post here, but hey, excerpt and link works just as well:

I never saw a man who looked
With such a wistful eye
Upon that little tent of blue
Which prisoners call the sky,
And at every drifting cloud that went
With sails of silver by.

I walked, with other souls in pain,
Within another ring,
And was wondering if the man had done
A great or little thing,
When a voice behind me whispered low,
'THAT FELLOW'S GOT TO SWING.'

Dear Christ! the very prison walls
Suddenly seemed to reel,
And the sky above my head became
Like a casque of scorching steel;
And, though I was a soul in pain,
My pain I could not feel.
Complete poem here