Quizzes are a fun way to test your knowledge of English. However, you won't actually learn much unless you understand why you got the answer right or wrong. So my advice is to favour quizzes that give you feedback on your answers.
Activities for ESL Students — Quizzes, tests, exercises and puzzles to help you learn English as a Second Language (ESL). This project of The Internet TESL Journal (iteslj.org) has thousands of contributions by many teachers.
English Language (ESL) Grammar Quizzes (UsingEnglish.com) — 518 free English language quizzes covering grammar, usage and vocabulary for beginner, intermediate and advanced level English students.
EnglishMediaLab — This site has quizzes for beginners, intermediate, and advanced levels.
ESL Quizzes (English Club) Test your knowledge of English with a quiz and have fun at the same time. There are quizzes for all levels - on grammar, pronunciation and vocabulary.
Free Quizzes for English Practice — Quiz categories include English Basics, Management, Sports, Dating, and Jobs. From EF English Live.
FlipQuiz — Gameshow-style quizzes created by educators. See my boards here.
ManyThings.org — Quizzes based on VOA programmes.
ProProfs — Quizzes on all sorts of general topics including Animals, Business, Food, Music …
Quiz Your English — Free app from Cambridge. Compete with other players from around the world and challenge your friends through social media.
Quiznet — Over 100 quizzes on all sorts of topics from the BBC Learning English archive.
Road to Grammar — 365 grammar and vocabulary quizzes (one for every day of the year!)
The English Blog — 113 posts categorized "Quizzes"