Three Perspectives on the Men in the Street: Texts of William Dean Howells's "The Midnight Platoon," Stephen Crane's "An Experiment in Misery," and Theodore Dreiser's "Curious Shifts of the Poor" from Sister Carrie.
Carrie Website at the University of Pennsylvania contains the
text of the novel, facsimiles of the typescript, and essays on the work
by distinguished Dreiser scholars. The general page for the
DreiserWebSource at this site includes photographs and a short movie
(in color) of Dreiser at Iroki. It also includes essays
on and lists of books in Dreiser's library.
On An American Tragedy
Note: Unfortunately, as of 2016, the State of New York has removed the trial transcripts and other materials at the links below. I'm leaving the links up in case they are reinstated in the future. In the meantime, here's a good article about the trial linking its details to Dreiser's novel: http://www.nycourts.gov/history/programs-events/images2/Judicial-Notice-11.pdf. See also Craig Brandon's Murder in the Adirondacks.
The Historical Society of the Courts of the State of New York includes information on the real-life Chester Gillette (Clyde Griffith in the book) murder case that inspired An American Tragedy, including a webcast lecture on the case and trial transcripts. The first 450 pages or so of the transcript focus on selecting jurors, etc.; the statement of the case concerning Grace "Billy" Brown (the Roberta Alden figure) begins in Vol. 1, p. 481. These can be compared with Dreiser's treatment of the case in An American Tragedy.
The site also includes page images of Dreiser's suit against Paramount concerning the 1931 film adaptation of the novel. [As of 9.6.17--this has also been removed.]
Works Available Online
Link to plain text or .html versions and some page image versions of all Dreiser's works available online at the Online Books Page: http://onlinebooks.library.upenn.edu/webbin/book/lookupname?key=Dreiser%2c%20Theodore%2c%201871-1945
Carrie (1900) (Online books page at U Penn)
An American Tragedy (1925; text in Australia; NO US ACCESS)
If you've ever wondered just how bad Dora Thorne is (according
to Ames in Sister Carrie), it's available at