One of my two favorites: Steak and kidney pie.
Not quite as good, but pretty much the same thing is a gentle braise in a brown mushroom sauce. This, and grilled (actually, sauteed) in bacon fat and served with bacon, and separately sauteed mushrooms both go very well with scrambled eggs.
They can be partially cooked, then coated with a breadcrumb, butter and mustard mixture (deviled), as you would a rack of lamb and grilled to a finish.
My other favorite: Simply grill them over charcoal and serve them with grilled tomatoes, bacon, mushrooms, and eggs scrambled with garlic chives and brandy and soda or iced coffee with brandy.
Veal, pig and lamb kidneys are mild compared to beef. Because they're so strong, you need to work with other tastes that will bland them -- like the pie thing, or the eggs. In any case they need to be prepped and blanched in milk. Beef kidneys need a longer soak.
To prep the kidneys, split them lengthwise, so you have two kidney shaped halves. Using a small, sharp, pointed knife, trim out the veins, the ureter, and all fat. Soak the kidneys in milk for at least an hour -- beef kidneys for several hours or overnight in the refrigerator.
IIRC I've got a recipe up for steak and kidney pie in a beef or steak pie thread somewhere on this forum. It should be fairly recent. If you can't find it, I suppose I can repost; or if you need some other specifics, not a problem. But once you've got the prep instructions and a few ideas you've got 91.4% of it anyway.