Simple present

http://www.grammar.cl/Present/Simple.htm

http://www.englisch-hilfen.de/en/exercises/tenses/simple_present_negation_sentences.htm
http://www.usingenglish.com/quizzes/65.html
http://www.aulafacil.com/CursoIngles/Clase6.htm
http://www.ego4u.com/en/cram-up/grammar/simpre-prepro
http://www.englishexercises.org/makeagame/viewgame.asp?id=714
http://www.englishpage.com/verbpage/simplepresent.html
http://www.englishexercises.org/makeagame/viewgame.asp?id=1052
http://www.perfect-english-grammar.com/simple-present-exercises.html
http://www.englishexercises.org/makeagame/viewgame.asp?id=1849
http://www.englishexercises.org/makeagame/viewgame.asp?id=4927
http://www.englishexercises.org/makeagame/viewgame.asp?id=5915
http://www.englishexercises.org/makeagame/viewgame.asp?id=7344