potato pancakes or what's referred to in our home as "baked potato soup" (just a basic cream of potato recipie i throw together but i add some cheddar cheese to, then we serve it topped with sour cream, chives and bacon bits).
if you want something kind of different, my mom used to make something called "mustard salad" with cold left over mashed potatos. she basicly used a potato salad recipie but replaced the mayo with mustard. it was tart but actualy pretty good when served very cold as a side with bbq or a sandwich.