I have a magnet plate hanging over my desk. Usually, the normal magnets for that purpose you can buy in shops are of very low quality and not very strong and fail to hold more than a few pieces of paper.

I recently discovered a way to get much better magnets almost for free: From old harddisks. To open a harddisks, you will usually need some kind of Torx screwdriver. Inside, you will find one or two very strong neodym magnets, which were originally used to move the read head.