Awakening 101
An excellent online course on the mystical experience. It begins with the premise that Enlightenment is outside the scriptures. The broad range of links available on various descriptions of "Zen" experience is very useful.
http://www.geocities.com/SoHo/Study/6309/awakening101.html

Ch'an Buddhism and the Prophetic Poems of William Blake
An essay discussing the relation between William Blake's poetry and Zen.
http://ccbs.ntu.edu.tw/FULLTEXT/JR-JOCP/ferrar1.htm

Logical Meanderings between West and East.
A comparison of Aristotle, Nagarjuna and Bhaskar.
http://www.wirehub.nl/chan/LM/LM.html

Religion of the Samurai: A Study of Zen Philosophy and Discipline in Japan and China
1913 classic book by Kaiten Nukariya. Complete online book.
http://www.sacred-texts.com/bud/rosa/index.htm

Zen Philosophy
A brief introduction to Zen thought.
http://goto.bilkent.edu.tr/gunes/ZEN/zenphilosophy.htm

On Zen Language and Paradoxes
A philosophical analysis of Zen koans by John King-Farlow.
http://ccbs.ntu.edu.tw/FULLTEXT/JR-JOCP/farlow.htm

Truth and Zen
A comparison of the Aristotilian view of truth and Zen's view.
http://ccbs.ntu.edu.tw/FULLTEXT/JR-PHIL/kasulis1.htm

Tsung-Mi and the single word "awareness"(chih)
by Peter N. Gregory, from Philosophy East and West.
http://ccbs.ntu.edu.tw/FULLTEXT/JR-PHIL/gregory.htm

The Zen philosopher: A review article on Dogen scholarship in English
The nature and importance of Dogen's thought as representative of the philosophical structure of Zen Buddhism.
http://ccbs.ntu.edu.tw/FULLTEXT/JR-PHIL/kasulis.htm