This one here from the Wisconsin Brat Pages (http://www.bratwurstpages.com/bratsides.html) is excellent:
German Potato Salad
5 pounds red potatoes, boiled until just tender with skins on
5 stalks celery, chopped
1 large onion, chopped
3/4 pound. bacon, cut in pieces about 1/2 inch
3/4 cup apple cider vinegar
2 cups water
1 cup sugar
1/3 cup reserved fat from cooked bacon
2 Tablespoons. flour
1/2 teaspoon. salt
1/2 teaspoon black pepper
2 teaspoons salt
While the potatoes are boiling, chop the celery and onions. Over medium heat, fry bacon until crisp. Remove bacon from pan, add onions to fat and sauté until translucent. To 1/3 cup fat in pan, add flour; cook and stir until just slightly browned. Add vinegar, water, 1/2 tsp. salt, and pepper. Cook and stir until clear and thickened.
Peel and slice potatoes while still hot. Add the 2 tsp. salt to the hot peeled potatoes. Add onion, celery and sauce to the potatoes and toss gently.