I immediately think of their products I use on a regular basis. There are so many.

  - micropore tape for mycelium and tissue cultures
  - reusable respirators and cartridges
  - net sanding disks
  - double sided tape for so many things
  - foam ear plugs and earmuffs
  - scouring pads for shop/kitchen/aquarium
  - HEPA air filters for work and home
  - command strips for all kinds of hanging and affixing needs
  - adhesive spray, mostly for wood working or working with templates 
  - stripping pads

The list goes on. There are alternatives from other brands, but a few of these are hard to compromise on and 3M does an incredible job. Their cubitron mesh/net sanding discs for example. I also like their respirator equipment too much to switch out another brand. Then finally it might seem insignificant but their double sided tapes are really good. When you find a bad one you never forget it, and similarly, you remember the good ones. 3M has been my favourite so far.