Grammar

a4esl.org  - This site has many self study quizzes on common grammar topics.

 

Englisch-hilfen.de  - Again, lots of grammar exercises.

 

Guide to Grammar & Writing - This site focuses a little more on grammar in usage rather than exercises. 

 

learnenglishfeelgood.com - Contrary to what this really horrible title suggests, this is a helpful website with lots of grammar quizzes.

 

Using English (ESL) Grammar Quizzes  - Lots of different quizzes.