It is well to observe the force and virtue and consequence of discoveries, and these are to be seen nowhere more conspicuously than in printing, gunpowder, and the magnet.
The mystery of magnetism, explain that to me! No greater mystery, except love and hate.
John Wolfgang von Goethe
Here are a lot of cool magnet experiments from the Magnet Man http://my.execpc.com/~rhoadley/magindex.htm
This series of pages from Trinity College in Dublin is fascinating! It's as much about the early superstitions as about the mechanics of magnetism. I learned a lot. Very readable. To go to the first page, click here.
Although magnetic lines of flux are invisible, iron filings will line up along them. Iron filings are a common waste byproduct of grinding in welding and fabrication shops. It is to metalworkers what sawdust is to woodworkers. You only need a handful or two to be able to see how the lines of magnetic flux radiate from the magnets into space and back to the opposite pole of the magnet. You can substitute some steel wool cut into very short pieces.
The least messy way to collect iron filings is to put a magnet in a plastic bag. Put the filings in a clear plastic bottle or jar. Shake the jar with the magnet pressed against the side and see what happens.
FLASH! I just found a similar but improved way to see flux lines from the Exploratorium. Click here.