If you want to screw with people, on some Windows setups, right-side Ctrl-Shift can switch from left-to-right to right-to-left text - easy enough to do in front of them without them catching it, plus you have to use the left-side to undo it. :>
Win+x, u u to quickly shutdown Windows. Although I've done this lots of times and not realised Notepad was open and my laptop has been on in my bag all night (my work one stays on when the lid is closed).
Not a keyboard shortcut but you can customise Explorer so it defaults to starting at This PC.
Found this useful whilst currently working from home over a laggy RDP connection to my work desktop PC, where every mouse move is slow. The less mouse the better.
Clear recent history (cache preselected). Maybe not my "favourite" since I only discovered it yesterday while doing frequent updates of cached JSON bits.