Some sites about Constructed Languages (ConLangs) and how to make your own language:
Omniglot (a site dedicated to languages and language learning)
http://www.omniglot.com/language/how.htm Ardalambion (complete analysis and learning instructions for Tolkien's languages)
http://www.uib.no/People/hnohf/ An outline for designing your own language:
http://www.zompist.com/kit.html A blog/news/resource site for ConLangs and real languages:
http://www.langmaker.com/db/Main_Page