First and foremost, my Juki 98Q. I don't know how I lived without it.
I LOVE my 60 mm rotary cutter. I seldom use the others since I started using it. Oh, I still do sometimes because I have the 45mm by my sewing machine, but for general cutting, I always reach for the 60.
And I do love the internet for all the info that is available.
There are others that I use, but some of those are interchangeable...but the three above are some of the ones I always go to. Right at this moment typing on here and talking to granddaughter so may not be thinking straight and think of something else after while.