I use an 8 x 8 scrapbook album to store my magnetic dies. I buy magnetic sheets at Oriental Trading
and slip them inside the plastic sleeves that come with the scrapbook album. I put a small label next to each one so I know what it's called and who the manufacturer is. So far it works for me, but it always seems like I'm on the hunt for something better. This is a great thread to see what others do.