http://www.englisch-hilfen.de/en/grammar/english_tenses.htm - English Grammar - Tenses
http://www.tolearnenglish.com/free/news/pdfg.php - Interactive tests
http://www.chompchomp.com/rules/irregularrules01.htm - Irregular Verbs
http://www.wordpower.ws/grammar/gramtoc.html - English Grammar - Table of Contents
http://www.pbs.org/speak/speech/verbmachine/irregular/ - AmEnglish - Irregular Verbs
http://www.tolearnenglish.com/free/news/pdfg.php - Interactive tests
http://www.chompchomp.com/rules/irregularrules01.htm - Irregular Verbs
http://www.wordpower.ws/grammar/gramtoc.html - English Grammar - Table of Contents
http://www.pbs.org/speak/speech/verbmachine/irregular/ - AmEnglish - Irregular Verbs