http://www.learnsite.ch/

http://www.ego4u.com/ 

http://www.past-simple.com/

Site about all the English tenses with great overviews and summaries. 

  http://www.englishpage.com

  http://www.english-4u.de

  http://www.englisch-hilfen.de/exercises_list/alle_grammar.htm

http://www.eclecticenglish.com/

  http://www.members.iinet.net.au/~adelegc/index.html