http://www.englisch-hilfen.de/en/exercises_list/verbs.htm
http://www.miguelmllop.com/practice/beginners/tenserevision/irregulars1.htm
http://www.miguelmllop.com/practice/beginners/tenserevision/irregulars2.htm
http://www.ego4u.com/en/cram-up/grammar/irregular-verbs
http://www.eclecticenglish.com/gapfillers/IrregularVerbs1A.html
http://www.eclecticenglish.com/gapfillers/IrregularVerbs1B.html