Things I'll always install on a fresh OS.
Every computer needs a web browser, and Firefox is the best one around at the moment.
Great tool for opening archive files from the internet, or compressing your own files to save space during backups. Much more space-efficient than Windows built-in zip tools.
A much more robust notepad with a smidgen of syntax colouring if you do some casual coding or config editing.
One of the best media players around, VLC strikes a great balance between having lots of features while remaining simple and intuitive.
Whlie not as user-friendly as VLC, sometimes you need something different. Whenever a file doesn't play nicely with VLC, I've found MPC-HC absolutely knocks it out of the park.
iTunes is bloated, other choices often have a 2006-looking UI or are just glorified file browsers, opening files from explorer is laughable... where does that leave you? MusicBee. I will admit MusicBee isn't perfect, but it's darn good.
Download almost any video from almost every website you can think of (yes, even that one). I get so much use out of this it's unbelievable.
Fully-featured screenshot tool, allows capture of your entire screen, a small region, GIF/video capture, all with quick editing and automatic upload. Extremely useful for quickly sharing ideas on messaging apps or forums.