Any scene with isolated elements much brighter than their surroundings is fair game. Expose for the bright lights so that everything else is suppressed and go to work. A 1/4 to 5 second exposure works well: it gives you enough time to do interesting things but not too much to really screw it up ;-).

My favorite, since I first got a decent camera as a child, has been the annual Christmas tree. You can shoot it out of focus:

(Front focus and back focus give slightly different shapes to the bokeh. The size is determined largely by how out of focus the image is, but it depends on the lens and the aperture too.)

You can move the camera around during the exposure:

Zooming during the exposure gives a characteristic effect:

You can do these in combination, such as this one that was unfocused while zooming:

Use your imagination and have fun!

Incidentally, it can be difficult to stop down a brighter scene. These images were taken at ISO 100 with apertures around f/11 for 1 - 4 seconds in a darkened room. An ND filter would be your friend with brighter lights (such as daylight at the end of a tunnel).