Road To Grammar is a site for ESL, TESL, EFL, TEFL, TOEFL, grammar and vocabulary practice (quizzes, extra practice, games, downloads for teachers and students... It includes answers and pdf documents).
You can also create your own quiz and host it on Road To Grammar
There is a version of Road To Grammar that has been cleaned up and made more attractive to younger learners for up to age 13: Road To Grammar Jr. http://www.roadtogrammar.com/junior/
On Twitter: @RoadToGrammar
R2G blog: http://r2g-r2g2.blogspot.com.es/