Academy of American Poets
Poets.org: A Brief Guide to Concrete Poetry
Concise explanation of the term "concrete poetry." It's mainly a discussion of the 1960s poetic movement, but it also includes the history of the term before and after.
Other
Centre for Literacy in Primary Education: Poetryline: Poetic Forms and Devices
An excellent resource for learning about the different forms and devices used in poetry. Each item is linked to its own page which has examples of its use. Many of the pages have videos of authors reading their poems, and some have...