Moving into our new office building, we spied a super cool feature in an upstairs office of a bunch of designers. On one wall they were using small metal magnets to hang all of their design drawings. Without piercing the drywall or needing to put up corkboard, they had simply painted the wall with magnetic paint which was extremely strong.
We went to Janovic to find it and they grumbled about it being discontinued, but when we spoke to the designers, they sent us this link. It's a good resource. Paint it on the wall as a primer - the more coats the stronger the magnetism - and then paint over with the color you desire. Available starting at $25 from Kling Magnetics in Chatham, New York. (Thanks, Travis!)