Good poems for ESL students?

What are some good English language poems to introduce ESL students to English/American poetry? Something not too abstract, with metaphors that are easily understood, something short. For example, Langston Hughes' "Dream Deferred" is a powerful and beautiful poem that could easily be discussed and understood by students of English as a second language whereas something from e.e. mings or John Ashberry may never be understood by someone whose native language is not English....