Thorough descriptions of the literary, socio-political and religious contexts in which Donne, Shelley and Keats lived and worked. Excellent background for understanding context of their writings.
The Poetry Archive is a not-for-profit organisation that makes and acquires recordings of poets from around the English-speaking world and makes substantial excerpts from them freely available online.
The Poetry Foundation is an independent literary organisation. They provide the full text of many famous poems and biographical and contextual information about the poets.
The Norton Anthology of Poetry by 
A History of English Literature by