Theory

Australian Nationalist Idelogical, Historical and Legal Archive - Documents relating to the Australian nationalist movement.
http://home.alphalink.com.au/~radnat/

The Nationalism Project - Academic site featuring articles and essays on nationalism.
http://www.nationalismproject.org/

Nationalism and its Discontents - In the wake of Osama bin Laden's global religious terrorism, old-fashioned nationalism is looking better and better. By Michael Lind.
http://www.washingtonmonthly.com/features/2001/0112.lind.html

Transformations of German Nationalism - Online dissertation arguing that there was no logical progression in German thought from the nationalism of Herder to the National Socialism of Hitler.
http://www.pganuszko.freeuk.com/dissertation/cover.htm

Nation Planet - A multilingual link site on nationalism, identity, separatism, regionalism, and ethnicity.
http://web.inter.nl.net/users/Paul.Treanor/plana.html

Modern History Sourcebook: Nationalism - Explores nationalism as a concept from a historical point of view. Links to source material such as important nineteenth century nationalist texts published online, including excerpts of Herzl's "On the Jewish State," Fichte's "To the German Nation" and Mazzini's "On Nationalism."
http://www.fordham.edu/halsall/mod/modsbook17.html

Nation, State, and Economy - Complete text of the book by Ludwig von Mises, discussing the nationality principle in politics, the effects of World War I, socialism and imperialism.
http://www.mises.org/nsande.asp

Reinventing Roots: New Media and National Identity - Paper by Dr. Piet Bakker of the Amsterdam School of Communication Research on the role of the internet in transmitting ideas concerning national identity.
http://users.fmg.uva.nl/pbakker/roots.html