I'm building one, too (see my other post). I decided to go with a 555 timer into a 4017 decade counter, which drives a circular array of super-bright white LED's. I've also found a place where I can get reflectors for mini-maglites for each of the LED's. The circuit is relatively straightforward. I've tested it on the breadboard and am in the process of soldering it more permanently. I'm also using a 120v photocell switch to turn on the power when it gets dark.
I think it will look very cool, will simulate rotation nicely, and doesn't have any moving parts to wear out. I think the white LED's will be bright enough to be noticed, but not bright enough to be annoying. Of course, you could use any color you wanted, or even a combination.
To make the beam a little broader and brighter, I'm using an array of diodes ahead of the LED's so that two neghboring LED's will be lit at one time as it circles around.