There are so many neat tubes out there.
One by one, I will add to this list as I go through my collection.

A miniature tube with a quartz crystal inside.  Used in some early color television sets.
Rather large mercury switch.
A Tune-A-Lite tube.  Although the tube works, the bulb is blackened on the inside, so the neon glow can only be seen from the tip end.  New or usable ones are extremely rare, and I haven't been lucky enough to stumble across one yet.  These were used as tuning indicators in radios before the magic eye tube was available.  Atwater Kent was one company to use the Tune-A-Lite, and advertised the feature as "Tonebeam".
An early 6H6 engraved metal tube with a flat top.
A tube engraved with the call letters WJAR on the base.
A Sylvania type SN4. updated! Thanks to generous feedback from several viewers, I now know that this tube is a neon filled strobe called a "strobotron", and may also be numbered 1D21 or 631-P1.  Following is a link to a very nice website with instructions for a project using this tube. Strobe project
An RCA JRC927 phototube.  Only three pins on the base.
A small 7 pin strobe tube used in precision timing equipment.
A German made 7 pin phototube tube used in early automated equipment.