Ethnologue Languages of the World Database - online database of information about 6,500 languages. Includes alternate names, number of speakers, location, dialects, linguistic affiliation, and other sociolinguistic and demographic data.
Foreign Languages for Travelers - provides vocabulary words, sound files with pronunciation assistance and a quiz to help you learn dozens of languages online.
Helpful Sites for Students - collection of informative links for students of languages. Languages covered include English, French, German, Italian, and Spanish.
I Can Eat Glass Project - a compilation of ways to say the phrase "I can eat glass, it does not hurt me" in many languages.
Indo-European - also includes recent books, conferences, and useful electronic resources.
Linguasphere - research network devoted to the study of multilingualism. Includes extracts from the Linguasphere Register - the first transnational classification of the world's speech communities.