1 or 2U Spacers
If you've ever dealt with a large rack with many devices screwed into it, you've probably run across 1 or 2U spacers that you can bolt in between 2 pieces of gear. These are often used to create a bit of space between 2 pieces of gear that might run hot or to cover up an empty section between gear instead of leaving an ugly gap. Someone should develop 1 or 2U spacer RE's so that I can separate devices in my rack when I see fit. That's what I need.