may/may not
http://www.english-grammar-lessons.com/maymight/exercise1.swf
must/have to
http://www.englishpage.com/modals/interactivemodal2.htm
could/might/should/would
http://www.englishpage.com/modals/interactivemodal6.htm
might/might not
http://www.english-grammar-lessons.com/maymight/exercise2.swf
practise with will/won't
http://www.tolearnenglish.com/exercises/exercise-english-2/exercise-english-15268.php
http://www.isabelperez.com/happy/tenses/exercises/will_1.htm