I go with wheatiefan's idea of the hard drive. I always keep a magnet from a hardrive on me. They are pretty strong and when I lose one I just go in my bin and get another. There are also some nice magnets in old phones. They are usually a small cylinder.
my scrap yard passes out those nice magnet keychains. It has their name on it so they can write them off as advertising and get their name spread around.
i find that harddrive magnets can be to strong and cumberoms for everyday use. If any one wants any i have at least a hundred or so for sale.
You don't want to put a magent on your key chain. When you unlock your car door it will hook on to the paint and scratch it. Also when walking down the freezer isle at the grocer your pants will stick to the coolers when leaning over. lol.