Other
Craft of Poetry: Quatrain
Site from a college poetry class that defines quatrain, gives some examples, and discusses some of the more popular [variations] as passed through tradition.
Academy of American Poets
Poets.org: Poetic Forms
This site shares numerous poetic forms. The following poetic forms are highlighted: rondeau, triolet, pastoral, pantoum, found, ghazal, dramatic monolgue, and blues.
Other
Bob's Byway: Glossary of Poetic Terms
Calling itself "unique," Bob's is easy to use, with cross-links throughout, phonetic pronunciation guides when necessary, and many examples and quotations. Click on the letter and scroll for the word.