Grammar exercises and explanations

Many exercises and rules (in German), very useful for practicing grammar

http://www.ego4u.de

Learning centre, test centre, online grammar

http://www.edufind.com

A variety of Print-out sheets with exercises

http://www.autoenglish.org/generalgrammar.htm

Printable Grammar Worksheets etc.

http://www.esltower.com/grammarteachers.html

http://www.esl-galaxy.com/grammarsheets.html 

Quizzes, tests, exercises

http://a4esl.org

Grammar, reading room, vocabulary

http://www.englishpage.com

For children, but nice exercises and information

http://www.kico4u.de/           

Grammar and vocabulary exercises

http://www.englisch-hilfen.de                                 

Grammar and vocabulary exercises

http://www.bbc.co.uk/worldservice/learningenglish/

Grammar worksheets

http://www.englisch-hilfen.de/arbeitsblaetter.htm

Interactive exercises with nice explanations

http://www.chompchomp.com/ 

An Internet grammar book for advanced learner plus some comprehension questions

http://www.ucl.ac.uk/internet-grammar/frames/contents.htm

A grammar website for beginners and intermediate students (nice layout)

http://www.roadtogrammar.com/

http://www.roadtogrammar.com/junior/

Grammar explanations with a lot of examples and some exercises

http://www.grammar-quizzes.com/index.html