Grammar topics (types of speech, verb tenses, free weekly lessons) http://www.englishpage.com/
English grammar lessons sorted by ability level: http://www.learn-english-online.org/
(This website is based in the UK, so some of the content will be different because they focus on British English.)
VOA: Leveled news articles with additional information for English learners: http://learningenglish.voanews.com/
Also from VOW: Let's Learn English is a new course for English learners. Certified American English teachers designed the course for beginners. The course continues for 52 weeks.
Each week, there will be a new lesson with video showing the lives of young Americans. The lesson includes instruction in speaking, vocabulary and writing.
There are also printable worksheets, assessments and lesson plans for individual learners and English teachers.
Podcast with a variety of topics for advanced level English learners (idioms, grammar, word choice, etc,):
Vocabulary Building: http://www.sheppardsoftware.com/vocabmania.htm
Fluency: Read more about ways to build fluency in this post.