This summer I went for some German language course in Goethe Institute in Berlin and had a chance to see many Palace and Castles in these two and a half weeks in Germany:
Charlottenburg, Sanssouci, Neues Palais (Friedrich der Grosse exibition), Glienicke,seen Babenhausen from outside, Cecilienhof, Schönhausen, Wörlitz, Oranienbaum, Mosigkau, Georgium, Köthen, Wernigerode, Arolsen, Wilhelmshohe, Hinter und Forderglauchau, Waldenburg, Rochsburg, Ludwigslust, Schwerin, Heidecksburg, Sondershausen, Obergriez, Untergreiz, Sommer Palais in Greiz, Eutin, Gottorf and Rossla.
I must say it was a wonderful experience! If one has any question about any of these Castles and Palaces, I'll be happy to answer...