The Trustee Library provides access to many different collections of articles which are excellent tools for academic research. Some of the best collections of literature articles are listed and linked below.
To paraphrase Whitman, this site contains multitudes: a searchable database of all editions of Leaves of Grass published during Whitman's lifetime; a growing database of poetry manuscripts; an excellent biography by Folsom and Price, with hyperlinks to an electronic edition of Walt Whitman: An Encyclopedia, ed. by J.R. LeMaster and Donald Kummings (1998); a large collection of contemporary reviews... The list goes on. Essential.