SOME THEORY WITH EXERCISES AT THE BOTTOM!
http://www.ego4u.com/en/cram-up/grammar/simpre-prepro
SOME PRACTICE
http://www.englishpage.com/verbpage/verbs1.htm
http://web2.uvcs.uvic.ca/elc/studyzone/330/grammar/simcon1.htm
http://web2.uvcs.uvic.ca/elc/studyzone/330/grammar/simcon2.htm
http://a4esl.org/q/h/vm/sp_or_pc.html
http://www.tolearnenglish.com/exercises/exercise-english-2/exercise-english-13846.php
http://www.englisch-hilfen.de/en/exercises/tenses/simple_present_progressive.htm
http://www.isabelperez.com/happy/tenses/exercises/present_cont_1.htm
http://madridteacher.com/Grammar/present-continous-activities.htm