Luminarium's Page on Marlowe
http://www.luminarium.org/renlit/marlowe.htm
An excellent starting point for Marlowe research. This page includes a substantial biographical sketch, many essays on Marlowe, and links to all of Marlowe's works online. There is a list of published works by and about Marlowe, and a list of his more famous quotations.
Perseus Project etexts
http://www.perseus.tufts.edu/Texts/MarloweTEXT.html
This collection of authoritative etexts includes Latin versions of the Dedicatory Epistle to Mary, Countess of Pembroke, and the Epitaph on Sir Roger Manwood. Included is a link to an Introduction, with textual notes and notations on words variant from these texts in other editions.
Marlowe Society
http://www.marlowe-society.org/index.html
This society, formed in 1956, is a registered charity dedicated to the research and furtherance of education about the "field of Elizabeth literature, and that of Christopher Marlowe in particular." It contains notes on all aspects of Marlowe's life and works, and gives considerable space to some of the conspiracy theories surrounding Marlowe.
Today in Literature's page on Marlowe
http://www.todayinliterature.com/biography/christopher.marlowe.asp
Biographical information, fiction, and lists of Marlowe's books and books about Marlowe.
PBS's page on Marlowe
http://www.pbs.org/shakespeare/players/player24.html
This is part of the "In Search of Shakespeare" feature on PBS, with Marlowe as one of the candidates for collaboration or outright substitution for Shakespeare as the writer of his plays and poems. Includes lavish graphics, and interesting facts about his life and death.