Sound and Sense by Laurence Perrine

Many editions, all excellent; probably the best general introduction to poetry (Howard Miller).

A Poetry Handbook by Mary Oliver

Another general introduction to the basic elements of poetry (Howard Miller)

The Poet's Companion : A Guide to the Pleasures of Writing Poetry by Dorianne Laux and Kim Addonizio

A highly accessible and enjoyable look at how to approach reading and writing poetry, with excellent suggestions and a list of very helpful writing exercises one may try after each section. (Rachel a.k.a. TheBroad)

The Sounds of Poetry by Robert Pinsky

Probably the best book on how sound is a constant element in all forms of poetry (Howard Miller)

The Situation of Poetry by Robert Pinsky

A great introduction into contemporary poetry and its traditions. A must read for those interested in the current and recent past states of poetry. (Shaun)

...likely to be overwhelming to beginners. (John Boddie)

The Triggering Town: Lectures and Essays on Poetry and Writing by Richard Hugo.

This book can assist beginning writers to think more clearly about their topics and the material they include in their poems. (John Boddie)

In the Palm of Your Hand: The Poet's Portable Workshop by Steve Kowit

A good general introduction to writing poetry of all kinds.(Howard Miller)

Creating Poetry by John Drury

This is a fantastic book for beginning and 'intermediate' poets. It covers fundamental language use and also sound, meter, forms, and many other topics. The author suggests numerous exercises throughout the book which are useful for the development of technique and imagination. (Mark a.k.a. Strangefire)

This collection of lectures by Milosz at Harvard provides a vibrant and engaging perspection on the path that poetry has taken in the Western world, how it has isolated the average reader, and what can be done to change this. Although Milosz uses anecdotes relating specifically to his own upbringing and life in Poland, the effect is universal. I found this book quite direct and accessible. It helps spur a poet to ask some crucial questions about one's own poetry, what it communicates and to whom, and how to make it vibrant in the real world. (Rachel a.k.a. TheBroad)