Some good books to draw from:
In the Palm of Your Hand, Steve Kowit
The Practice of Poetry, ed. Behn & Twichell
The Poet’s Companion, ed. Addonizio & Laux
The Poetry Home Repair Manuel, Ted Koozer
The Triggering Town, Richard Hugo
Writing Poetry, Barbara Blake
Writing Poems, Wallace & Boisseau
A Poetry Handbook, Mary Oliver
A Poet's Guide to Poetry, Mary Kinzie
Online Sources:
Kalliope Poetics - An online poetry "exercise library" that lists tips and exercises on everything from image to point of view, concrete poetry to formal verse.
Everybody Writes - A fun page of exercises geared for children but inventive enough for any playful child-at-heart poet.