How about using two poems from the same poet? Dylan Thomas has some great pieces that would work well, as do Edgar Allan Poe, Emily Dickinson, and Walt Whitman. Or, how about contemporaries rather than classics; Maya Angelou or Shel Silverstein?
You could discuss themes, structure, tempo, subject matter...just about anything you could think of. Or, you could take two poets from the same time period, such as William Butler Yeats and Oscar Wilde and compare/contrast their works according to the same criteria.
There are countless poets out there, so pick two pieces that you find interesting, and take your time; there will be plenty of material once you get started.
Best of luck!