Páginas Educativas:

ESL printables: English language worksheets, powerpoints, online exercises, etc.
ESL Printables is a community of ESL teachers who share their own resources. If you want to download worksheets or powerpoints, you have also to contribute with your own creations.

English Exercises .org
This is a web page with thousands of free exercises to practice English language online.

Magic Vocabulary
Magicvocabulary.net is an automatic generator of worksheets and online games, with your own word lists.