This year for the Vancouver Maker Faire I build a Compass table that I found on instructables.com. I found a cheap price on 1000x compasses from alibaba.com for about $0.10 each. I found the wooden table at thrift store for $20 and two sheets of acrylic.
I made the square acrylic version first as a test to see how the table would look. Afterwards I constructed the table. The whole thing took about an hour.
Here is an image from Maker Faire with some kids playing with the table. I put the magnets in to some knex and attached strings to them so people would not walk off with them.
Finished and sitting in my living room