If you really want a cruiser, look at an Electra Townie. I think they come mostly with a 3spd internal gear hub, but those are low-maintanence. Their bikes look really durable and should provide you with what you are looking for, a simple comfortable bike to just get around town and get some exercise in!

You say single speed, but do not over-look the Internal Gear Hubs, like the townie I mentioned. They keep the maintanence low, but provide more of a gear range than a single speed. Coaster brakes work rather well, too, and have for many years