Note: I cannot personally vouch for the quality of all the materials offered on the external sites listed here. Some are more useful than others. Use your own best judgment.
To report errors or to recommend sites to add to this list, please contact me.
» Amaravati Buddhist Monastery (Amaravati Buddhist Monastery, UK; PDF and HTML) offers a chanting guide and books by monastics from the Amaravati Buddhist sangha.
» Aruna Publications (Aruna Ratanagiri Buddhist Monastery, UK; PDF and HTML) offers chanting guides and books by monastics from the Amaravati Buddhist sangha.
» Beyond the Net (Damrivi Foundation, Sri Lanka; HTML) has a collection of good short introductory articles about Theravada Buddhism by such authors as Bhikkhu Bodhi, Piyadassi Thera, Mithra Wettimuny, and Lily de Silva. (Warning: this site makes heavy use of frames, graphics, and applets. Extra patience required.)
» BuddhaNet (Buddhanet, Australia; PDF, HTML, and other formats) has a large archive of Buddhist texts in a variety of formats.
» BuddhaSasana (Binh Anson; HTML) offers a good selection of articles and translations by contemporary authors (mostly Theravadan), in a very readable format.
» Going Forth (Malaysia) offers a collection of links to sites offering personal reflections on life as a Theravada Buddhist monk or nun.