Tensebuster is a more interesting way to study grammar in context. There are five levels from beginners up to advanced, covering many common grammar points. Each unit includes listening and reading texts, practice in context, self-tests and ideas for how to practice each grammar point in real life. http://www.hkbu.edu.hk/lib/electronic/elearn.html - go to ‘Language Learning’ (For HKBU users only)
Grammar-Quizzes contrasts points of grammar and provides examples, explanations, practices and interactive quizzes for adjectives, verbs, prepositions, clauses, phrases, expressions and much more! http://www.grammar-quizzes.com/index.html
Postscript is an online magazine especially to help English learners with business English. You can choose exercises according to topic, or select from the vocabulary, grammar or reading links. http://www.linguarama.com/ps/index.htm
Click on the ‘Common Errors’ link to find many exercises on grammar and vocabulary errors commonly made by Hong Kong students.
This site is part of Hong Kong Polytechnic University's writing site on Help with Final Year Projects. http://elc.polyu.edu.hk/fyp/
This program is specifically designed to help you prepare for the IELTS examination, but will also help with general study skills required for higher education. The ‘Grammar’ module covers key grammar points in academic reading and writing and also helps you isolate and work on your own grammar errors. http://www.hkbu.edu.hk/library/electronic/elearn.html - (for HKBU students only) to find out the username and password and access the program - choose ‘Language Learning’
Click on ‘Structure Test 1’, ‘Structure Test 2’, or ‘Structure Test 3’ for three proofreading tests. Based on the old TOEFL grammar test format, these tests cover grammar errors often made in students ‘ academic work. http://www.examenglish.com/TOEFL/index.php
This business English site by Hong Kong Polytechnic University has a section on grammar and vocabulary errors often made by Hong Kong students.
Scroll down to the heading ‘Writing Workplace Correspondence’ and you will find many links to different grammar points. http://elc.polyu.edu.hk/eiw2/TOC.htm#htm#02
Part 2 (Usage: Chapters 8-15) of this online textbook in basic writing focuses on common written grammar errors. It has many interactive exercises to help you improve your writing skills. http://www.ccc.commnet.edu/sensen/index.html