This page contains links to sites that I think will be useful for English learners. Please contact me if you would like your site added to this list.
Really Learn English has a lot of free resources, as well as a good store with lots of decent learning material.
H2English is obviously a labour of love and you should have a look at this site.
ESL Academic Writing Skills tackles writing, one of the more difficult subjects to improve online. Does a great job, so check it out.