All the Japanese Slang You Can Stand - Dictionary of slang terms, with an introductory page offering general advice and book recommendations to people interested in learning Japanese.
The Japanese Language - Gives a linguistic look at Japanese, its classification, and its changes from adoption of Chinese characters and development of its own syllabaries.
Japanese wa, mo, ga, wo, na, no - Scholarly study of the syntax of the six most common post-nominal particles in Japanese, by Frederik Kortlandt.
The Kanji Master Program - Site devoted to the study of kanji in the light of their history and place within Chinese and Japanese civilization.
Kanji Names Project - Descriptions of Japanese names in English with kanji image files, and information on kanji books.
Kanji.com - Writings on the kanji character system.
Keiichiro's Home Page - Features lengthy list of "Janglish" words used in contemporary Japanese, including their pronunciation and meaning, as well as brief articles on features of English confusing to a speaker of Japanese and examples of Japanese brand names.
My Furusato - Features eight basic Japanese lessons, stories, Japanese proverbs related to smiling, and miscellaneous personal features.
Nihongo: Japanese Language - Articles reflecting on miscellaneous aspects of the language, thorough resources for Japanese numbers and counters, and lengthy list of summaries of books for learning Japanese.
Origins of the Japanese Language - Presents a theory on the origin of the Japanese language, addressing issues of whether it is an isolate and its relationship to surrounding languages.
Otake Japanese Calligraphy - Pictures of kanji characters and their meanings in several categories. Also features a list of many common English names transliterated into kana characters.
Reading Tutor Homepage - Designed to help JFL/JSL learners improve their reading skills in Japanese. Has bilingual dictionary; vocabulary and kanji level checkers.