Bibliography of Planned Languages (Excluding Esperanto) - - List of books on interlinguistics, Volapük, Ido, Ro, Occidental, Novial, Interlingua, Glosa, modified English and Latin, pasigraphies, number languages, and other planned languages.
Conlang Free City - - This Conlang Wiki is devoted to the topics of ConLangs and ConCultures. This is an online resource and communnity about Conlangs that you can edit.
Conlangs DE-Cal - - A class on constructing languages at the University of California Berkeley.
Constructed Languages - - An encyclopedia entry describing constructed languages, including sections on auxiliary languages, artistic languages, and logical languages.
Constructed Languages - - Links to many conlang sites as well as the author's own conlang.
Phonetic Picture-Writing - - Phonetic picture-writing can also be read phonetically. Its ideograms are composed of special letters. Authored by Leonhard Heinzmann.
Studoj pri Interlingvistiko / Studien zur Interlinguistik - - Journal article by Wim Jansen that reviews a book on language planning and language policy by Sabine Fiedler and Liu Haitao. The book is on the theoretical and applicational aspects of interlinguistics, esperantology, terminology and lexicography. [PDF.
Universal Language Dictionary Project - - An attempt to create a list of concepts, described in English, along with words to express those concepts in several natural and artificial languages.