Agendaweb.org website is a great source for ELT. This
site categorizes the activities (Vocabulary, Grammar, Listening, Speaking,
Writing) and also the levels (by using colours). You can also download
worksheets. Please add more links as a comment, so that we can add it
here.
Englishgrammar.org website is a great source on grammar. You can easily find every grammar topic and the website has lesson plans, online exercises, online tools, videos and writing guides. You can get free updates by adding your email address or you can follow in Twitter @GrammarUpdates