An updated sixth edition of James L. Harner's book An Annotated Listing of Reference Sources in English Literary Studies is now freely available online via GitHub (https://oncomouse.github.io/literary-research-guide/). The Murdock Library has a print copy of the third edition at PR83 H34 1998.
The following list is meant to be a survey of reference titles recommended by your professors and librarian. It is not meant to be exhaustive. For more possibilities, check out the reference databases linked on the left of this page. If you ever encounter a reference citation in a database without full-text access, make sure to check to see if a print copy is available via Summit or Interlibrary Loan (ILL)