Wow - you should join this site if you are a German teacher/learner! It has LOADS of online activities to practise your German not to mention current topics and competitions! Check it out!
I have just uploaded a couple of videos onto youtube going through some German grammar. At the moment I have done accusative and dative pronouns and adjective endings following indefinite articles.
On-line verb conjugator. Includes the following languages:- English, French, German, Italian, Portuguese and Spanish.
There are training exercises too.