I'm sending you some web pages that I find particularly useful, and some notes about them so you can visit only the ones you find interesting.
Looking forward to hearing from you all!
http://www.isabelperez.com/ (a very complete page, Isabel's work is just astonishing: lots of useful exercises, activities, grammar exercises and explanations... two thumbs up!)
http://www.agendaweb.org/ (full of useful and interesting resources)
http://www.onestopenglish.com/ (maybe not as good as Isabel's, but with different exercises)
http://www.howjsay.com/ (this web side helps you (and your students) with the pronounciation, but not only of words, but of expressions, whole sentences, and so on.)
http://www.dixio.com/ (this web page contains not only a very powerful and good dictionary, but also you can sign in for 'the word of the day' (in the English version, not the Spanish one) and they send you a word everyday, with the explanation of its meaning, origin, use, etc. I use the most interesting ones in some of my classes as a warm-up activity.)
I hope you find them useful too.