American Verse Project (Univ. of Michigan)   

Bartleby's Verse Search (Includes Oxford Book of English Verse, Yale Book of American Verse, and volumes by Emily Dickinson, T.S. Eliot, Robert Frost, John Keats, and many other poets.)

British Poetry 1780-1910 (University of Virginia)

The CMU Poetry Index of Canonical Verse

Dream Machine's Web Poetry Corner (Contemporary poets and their poems)

International Poetry Sites

Modern and Contemporary American Poetry 

PIZZAZ! -- Limericks to haiku to quatrains. A website designed for ESL students

RhymeZone -- Find rhymes, homophones, and synonyms for English words

Sonnet Central