[DonRotolo]

As already said, every magnet has a north and south pole. One of the major searches underway in nuclear physics is for "the magnetic monopole": If one can be found, it will tie up some loose ends in the grand unification theory, helping equate gravity to magnetism (and therefore electricity). Can you say anti-gravity??

Strongest means magnetic flux density. The absolute strength is the same at both ends, kind of like the current in a simple DC circuit, but you can modify the flux density (measured in Gauss) by physically changing the shape of the magnet, or channeling the magnetic flux to a point. (For example, make an electromagnet from a nail. The pointy end will appear 'stronger' than the flat end)

Mu metal is indeed a great magnetic shield. For cheap, find a TV and take the metal shielding near the picture tube*. The better a material 'conducts' magnetism, the better of a magnetic shield it is - just like electrical shielding. "Shielding" just gives the magnetic (or electrical, or whatever) field an easier place to travel, and so you direct it around whatever object you are shielding. Steel is not too bad a shield, for the cost.

* Warning: The picture tube has high voltage, and acts like a capacitor to store it for quite a long time. Stay the heck away from the high voltage wire to the picture tube (which looks kind of like a spark plug wire) and any connectors to same.

Buying magnets: American Science & Surplus, plus those already mentioned.

Don