T. S. Eliot is such a major figure in 20th Century culture that it would be impossible to cite even a partial list of useful works that make his own writings more accessible.
However, as a way into his "Waste Land," this article by R. V. Young does an excellent job of helping one see the grand view of Eliot's purpose in this most difficult poem, and the article also provides numerous helpful coments of specific lines and images.