Passive Voice

Easy exercises:
http://www.ego4u.com/en/cram-up/grammar/passive
http://www.tlumaczenia-angielski.info/angielski/tests2.htm


Mixed tenses:
http://www.ego4u.com/en/cram-up/tests/hadrians-wall
http://www.learnenglishfeelgood.com/esl-passive-voice-exercise2.html
http://www.englishexercises.org/makeagame/viewgame.asp?id=1213
http://www.englishexercises.org/makeagame/viewgame.asp?id=4443 
http://www.glohima.com/BACKUPACTIVITIES/GRAMMAR/B2/PASSIVE/ThePassive.htm

Good luck!