Friesian School
Friesian.com: Immanuel Kant (1724 1804)
This extensive site chronicles modern philosophy and the role of Kant in the movement. Excellent resource.
Stanford University
Stanford Encyclopedia of Philosophy: Friedrich Nietzsche
A thorough, insightful overview of Nietzsche's life and works. A superb introduction.
Internet Encyclopedia of Philosophy
Internet Encyclopedia of Philosophy: German Idealism
An excellent breakdown of the development of German Idealism. Refers to each of the important thinkers, and their inter-relationships.
Friesian School
Friesian.: Arthur Schopenhauer
Good introduction to Schopenhauer's basic ideas at this site from Friesian.com. Two useful charts in particular illuminate his philosophy. Presented from the point of view of Kantian philosophy.