I've been using these for years in physics lessons - it is a good demonstration of Fleming's left hand motor rule.

There are a couple ofproblems though.

It can be difficult to see the motion from the back of the class.
It won't run unattended.

I remixed this from here

Step 1: Ingredients

A retort clamp orsome other way of holding the battery up;
A washer;
Two rare earth magnets;
A spinner;
A wire;
A wood screw. (must be ferrous Metal).

Step 2: Make a Spinner.

I found an image of a spiral (in the public domain). I cut and pasted it into an editor, and printed it out.

I then cut two circles out and glued them back to back.

Step 3: Assemble the Motor

Assemble the motor in the usual way as shown in the original instructable,

The differences are

1. the addition of the spinner and the washer that makes it stick to the magnet.
2. The use of the clamp to hold the battery. (So you don't have to)
3. A second rare earth magnet is used to attach the wire to the top of the battery

Normally if you were making one of these motors you would try to make everything as well centred as possible.

In this case you actually want to make the assembly slightly off centre. This means as the disk spins, the lower magnet will tend to lose contact with magnet. Thus it will spin slower and in an eye catching wobbly manner.