For a small box just drill a blind hole into the wood on each side and inset a rare earth magnet into the holes with a dab of glue. Make sure you pay attention to the direction of the poles and it holds just fine. I’ve bought several times from these folks:
http://www.magnet4less.com/
Kind of a goofy website, but they have good prices and the products have been accurately described. I’ve used these for latching:
http://www.magnet4less.com/product_info.php?products_id=90
For cabinet latches of various kinds here is a site that aggregates links:
http://www.thewoodworkingcatalog.com/hardware.html