Here are some cool things that don't quite fall under other topics.

• Battlefield Periscope

Battlefield Periscope

A cool for seeing LOS from the miniature's perspective without knocking things over leaning into the battlefield.

• Tabletop Periscope for Wargames - On Major General Termorden Rederring's Colonial Wargames Page; this is well documented, including building diagrams and a dash of physics. :-)
• TerraGenesis LOS-O-Tronic - inspired by the Major General, this is a sci-fi version, made for Warhammer 40k use. Same beast, different hide.
• Cottage Periscope - another one inspired by the Major General. This is a very crafty version, made to look just like a building. Again, same beast, different hide.

Buying supplies for this is pretty straightforward. The trickiest part is the mirror. Don't waste your time and energy trying to find 2" x 3" mirrors that are already made. I went down to Home Depot (a local DIY warehouse store) and bought a single 12" x 12" pane of mirror for a whopping $2. Ideally, a glass store would be the place to get it cut into pieces. You can also try a hardware store. I ended up at a framing store, under the assumption that they have to make prety cuts of glass for their picture frames and I was right. They happily chopped it up into 24 pieces of 2" x 3"; periscopes all around!