Last month it was a new poem by Robert Frost, and today (to-day) we have an unpublished sonnet by Sylvia Plath.
The poem, "Ennui," appears in the online journal Blackbird, a collaboration of Virginia Commonwealth University's English department, and the New Virginia Review. It was discovered by Anna Journey in the Sylvia Plath Archive of juvenilia in the Lilly Library at Indiana University.
Along with a nice introduction, Blackbird provides images of the original typescripts (early and final drafts). (Via scatteredpaper.)
Update: Charles Bainbridge, of The Guardian, offers an insightful little explication of "Ennui."