Links
http://hometown.aol.com/ekphrasis1/ - The homepage for Ekphrasis: A Poetry Journal.  Ekphrasis is a biannual publication printed in Sacramento, California.

http://www.puddinghouse.com - The official site for Pudding House Publications, a company which has printed a number of ekphrastic works within the past few years.

http://www.puddinghouse.com/ekphrastic.htm - A comprehensive ekphrastic page on Pudding House's website.

http://www.people.virginia.edu/~djr4r/anth_poems.html - A website that has the full-text and images for a few of history's better-known ekphrastic poems.

http://web.ics.purdue.edu/~clark9/ekphrasis/ - A website created by Tracy Clark, an employee of Purdue University's Professional Writing Program.

http://www.poemeleon.org - An online literary magazine which accepts submissions year-round.  The editor often has themed issues, and has previously printed an issue devoted to primarily ekphrastic poems.

http://www.english.emory.edu/Paintings&Poems/ - A website created for a course at Emory University.  Contains several ekphrastic poems and images by American authors.

http://www.qarrtsiluni.com/ekphrasis/index.html - Qarrtsiluni is an online literary magazine.  The publication runs various themes, one of which is ekphrasis.

http://poetryaboutart.wordpress.com/ - A blog by poet Therese Broderick, created to draw attention to examples of contemporary ekphrastic poetry.
Other Resources
As with any poetic mode, the best way to learn about it is to read it.  Some of the major players in ekphrastic history are many of the classic authors that you may already know and love: Homer, Virgil, Keats, Shakespeare, Wordsworth, Byron, Shelley, Yeats, Plath and so on and so forth.  There are also many contemporary poets that may not line your bookshelf, but certainly will leave a mark on the pages of literary history.  One of the of the most widely known contemporaries is Sharon Dolin, her anthology Serious Pink serves as a good start for anybody interested in contemporary ekphrastic poetry.  Other possible resources are The Magic Fish by Jennifer Bosveld, Wisconsin Poets at the Elvehjem Museum of Art edited by Russell Panzcenko, and Transforming Vision: Writers on Art edited by Edward Hirsch.  Another possible resource is Ekphrasis, a literary journal based out of California, which is filled with the latest offerings of contemporary ekphrastic poets.  For a closer look at some historical ekphrasis you can read just about any piece of ekphrastic criticism written by James Heffernan, or check out any of the other books listed below.  All of the books listed below pick apart various aspects of ekphrastic poetry, but of all the books listed two are probably the best place to start: Museum of Words and The Gazer's Spirit give the most essential information.

Museum of Words: The Poetics of Ekphrasis From Homer to Ashbery, written by James A. W. Heffernan.

The Gazer's Spirit: Poems Speaking to Silent Works of Art, written by John Hollander.

Sculpted Word: Keats, Ekphrasis, and the Visual Arts, written by Grant F. Scott.

Museum Mediations: Reframing Ekphrasis in Contemporary American Poetry, written by Barbara K. Fischer.

Getting the Picture: The Ekphrastic Principle in Twentieth Century Spanish Poetry, written by Margaret Helen Persin.

Literary Realism and the Ekphrastic Tradition, written by Mack Smith.

Literary Objets d'art: Ekphrasis in Medieval French Romance, written by Linda M. Clemente.

Iconcs, Texts, and Iconotexts: Essays on Ekphrasis and Intermediality, edited by Peter Wagner.

The Shield of Achilles and the Poetics of Ekphrasis, written by Andrew Sprague Becker.

Colors of Rhetoric: Problems in the Relation Between Modern Literature and Painting, written by Wendy Steiner.

Text As Picture: Studies in the Literary Transformation of Pictures, written by Hans Lund.

Ekphrasis: The Illusion of Natural Sign, written by Murray Krieger.

Crossroad of Arts, Crossroad of Cultures: Ecphrasis in Russian and French Poetry, written by Maria Rubins.