British National Corpus - online corpora that contains 100 million words of texts
English Club - a website that helps you learn or teach English with various lessons
Englishleap - a website that offers lots of free resources for learning English online with grammar and vocabulary exercises
ManyThings.org - a website that contains interesting resources for ESL(English as Second Language) students
Merriam-Webster Online - Dictionaries and Thesaurus online
The Internet Grammer of English - an online course in English grammarwritten primarily for university undergraduates
Chinese-English Dictionary - Searchable dictionary with options for English, pinyin, and Chinese queries
Chinese for Beginners - Peking University - an ABC Chinese course for beginners, including introduction of phonetics and daily expressions
Oxford Language Dictionaries Online - Searchable comprehensive bilingual dictionaries in Spanish, French, German, and Italian
Spanishdict.com - Popular Spanish-English Dictionary online
NHK World Japanese Lessons - Basic Japanese audio dialogues you can download free along with downloadable lesson transcripts.
Compleat Lexical Tutor - For data-driven language learning online
Duolingo - Learn a language (Spanish, Japanese, Chinese, French, German, Korean, etc.) for free. Forever.
Memrise - the place to go for your vocabulary retention via a lot of courses on almost every language
WordReference.com - a forum that contains the largest repository of knowledge and advice about the English language, as well as a number of other languages