BBC Grammar Challenge

• Weekly radio program focusing on grammar.  Listen to the program, read the explanations and take quizzes

BBC Skillswise English

• A  collection of resources designed to improve your English, including sections on reading, writing, spelling, word grammar, sentence grammar and speaking and listening.

Common Errors in English Usage

• Comprehensive, and some may say picky, guide to English usage errors

English for Business Success

• Free online textbook aiming to improve  your written communications and writing proficiency

Grammar Girl

• Website and podcast proving "quick and dirty" tips to better writing

Grammar Infographics

• A large collection of grammar-related infographics

Grammar Monster

• Free Grammar Lessons and Exercises

Grammarly

•  Online text editor with grammar checker, spell checker, and plagiarism detection

Guide to Grammar and Writing

• This guide contains good advice on grammar and English usage, quizzes, recommendations on writing and help with argumentative essays.

Homophones

• Homphones are words that are spelled differently but sound the same.  These three videos from MSLETB discuss some common homophones
  • There/Their/They're
  • To/Too/Two
  • Other homophones

Mac and Rory's Grammar Stories

• This is an English grammar reference guide specifically designed for kids, but anyone who wants to improve their grammar can use it.

NALA - Brushing up

• A learning support workbook that covers the basics of spelling, grammar and punctuation

Perfect English Grammar

• More than 400 free exercises and explanations, which you can use to improve your grammar

Road to Grammar

• Quizzes, games and exercises focused on English grammar and vocabulary.

The Oatmeal - How to Use an Apostrophe

• The Oatmeal is a very funny web comic. This strip illustrates the correct use of apostrophes

The Oatmeal - How to Use a Semicolon

• As above but for semicolons ("the most feared punctuation on Earth")