I have seen a number of blogs and articles out there on this topic, but I thought I would add to the discussion:
How to Magnetize the Mars Attacks Big Stompy Robot:
A couple of articles out there:
So here is what I am working on:
I wanted to be able to rotate the arms at the shoulder and elbow joints. Looking at the model, I thought 'hey, maybe a washer would fit around the elbow joint!?' So I found some washers that would fit:
8mm Flat washers fit perfectly. To ensure they wouldn't interfere with rotating the arm, I used some snips to trim the washers slightly.
Then I glued the washer on using Army Painter superglue.
Then I drilled the elbow joint on the upper arm and put in 1/8" magnets. They were small enough to fit and I used two in order to ensure they would hold the weight.
Next I used some larger, flat disc magnets in the shoulder joints.