Thought I'd jump into the fray with a few more restaurants....
For Milwaukee, Maders, Karl Ratzsch, and Weissgerber's have already been mentioned. However, Bavarian Inn in Glendale (a suburb) is quite good: http://www.bavarianinnmilw.com/
Unfortunately, their hours are very limited: Tuesday and Friday for lunch, Sunday for brunch, and Friday for dinner. The place makes more business as a banquet hall, thus limiting sit-down hours.
There are other restaurants in Milwaukee that are more "German style" or "German-American" than strictly German, such as Kegel's Inn: http://www.onmilwaukee.com/dining/articles/kegelsinn.html
Also in this group is Pandl's in Whitefish Bay, another suburb: http://www.jackpandls.com/
Other places with some German items are Turner Hall and Old German Beer Hall, both downtown.
For Buffalo, NY, someone already mentioned Scharf's Schiller, but Ulrich's Tavern (north of downtown in the ECMC area) also has some good German items going. And the atmosphere is fun: http://www.ulrichstavern.net/index.php