Reading regularly in English is one of the best, cheapest and easiest ways to improve your level of the language. The problem with reading things in English is that it can be difficult and frustrating to find things which are right for your level (some things will be too easy, while other things will be too hard).
To help you easily find articles which are right for your level, I have created the two below lists of online articles (one for people whose level is intermediate and the other for people whose level is upper intermediate).
In addition to each of the articles in each of the lists, you will also find an exercise which will help you improve your use and knowledge of English vocabulary.
If you are a teacher and want to use these article exercises with your students, I recommend that you read a guide I have written which explains the best way to use them in class.