We've been asked a couple of times to recommend some additional resources for learning English (especially grammar, which can be notoriously tricky and irregular). I'm one of the English linguists who developed the Estonian > English course. Here's a short list of websites (that I've personally used at one time or another) to make your use of English the best it can be.
Have you used any of these resources? Or do you have any interesting links to add to the list? Tell us in the comments below!
Learn English by the British Council
One of the most popular and enthusiastic communities around the world. In addition to learning about English grammar, you can also use games and exercises to develop your writing skills and listening comprehension.
English Grammar Secrets
Every topic is followed by an exercise, so you can practise what you've learnt.
A super useful website for both beginners and advanced learners. If you can't find an answer to your question, Jennifer (the author of the site) is always happy to help out.
A fantastic resource with many examples (both correct and incorrect, so you'll know which errors to avoid).
Lots of printable lessons on various topics.
Quizzes... So many quizzes...
Perfect English Grammar
Tips for learning grammar and improving your language skills.
English Teacher Melanie
Lessons that deepen your understanding of natural spoken English.
Thorough grammar explanations combined with answers to learners' frequently asked questions.