You may already be familiar with the following websites, or this might be your first introduction. Either way, each of them can be a ready source for you.
English Lessons and Tests. Reading, grammar, vocabulary.... divided by difficulty levels.
Interactive ESL Practice Practice your grammar and vocabulary
ESL Quiz Center (from Dave's ESL Cafe) Grammar, Geography, History, Slang, Science
Vocabulary Training Exercises In English, German, French and Spanish
Vocabulary, Word Puzzles and Activities Helps prepare for PSAT/NMSQT*, SSAT*, GED*, SAT* and ACT* tests
ESL Resource Center Exercizes and language lessons.
ESL quizzes for English learners. ESL Quiz Centre at englishclub. Quizzes for all levels on grammar, pronunciation and vocabulary.