I don't have any of my poetry books here at work, but off the top of my head some of my favorites that I can recall:
"Because I could not stop for death he kindly stopped for me" - Emily Dickenson
"Lenore" and "Anabel Lee" - Edgar Allen Poe
"Father" - Sylvia Plath
"O Captain My Captain" - Walt Whitman (fuck you, i like it)
And there's one really long poem that has "the center cannot hold" and "things fall apart" in the middle of it somewhere and I could kick myself for not remembering what it was or who wrote it
sadie would know, I'll bet
There are lots of others but it's hard to remember without a book right in front of me. I have the Oxford Book of American Verse, and that thing kicks ASS. So much good stuff in there.
EDIT: There was some other poem written by a World War I combatant that I really liked (about the war), but I can't remember much about it at all