Spectrum toys are fun to experiment with. You can light them up with a high voltage field or even a tesla coil. This Spectral Tube Group kit comes with 6 gas tubes and a convenient holder. You can light them up all the same time.
These spectrum tubes are a bit shorter than your average 26cm tubes. You get Nitrogen, Argon, Helium, Neon, Hydrogen, and Hg tubes that turn into a rainbow of colors in the dark when excited.