Arbor Farms is my favorite grocery store in Ann Arbor, and their hot-food counter is fantastic. I recently bought their weekly special, which was a vegetarian Reuben with marinated tempeh, sauerkraut, onions, and vegan dressing. It was excellent. If they don't have a similarly veggie-friendly special when you're there, buying one of their chickpea walnut burgers (vegan warning -- it has eggs) and crumbling it atop a side salad is always a good bet. The homemade balsamic dressing is awesome.
For out-of-towners, this is a good chance to sample some locally grown food. It's cheaper than Plum Market, and the hot-food options are MUCH more vegetarian friendly.Pros: Local produce, Great hot bar, Locally owned