from Ikea, and a package of 3 is $4.99. These containers are larger than I expected, and the lids fit very securely. They have an extra large magnet on the back so rest assured it won't fall off your magnetic surface.
I used my labelmaker (free after rebate at Staples a few years ago) to make clear labels for each container.
I chose to put my spice containers on the side of my refrigerator. My kitchen isn't that large, and this area of my refrigerator is easily accessible when I'm cooking or baking. I have seen others put them on a cookie sheet and lean it against a cabinet or backsplash, or you could have a piece of metal cut to fit on the inside of a cabinet door. Whatever works for you. But, for me, the magnetic space on my fridge was already paid for and involved no extra trips to the store. :) I also feel like it's a form of artwork in my kitchen... functional artwork.