When I started quilting about 10 years ago, I found a 6-1/2" x 24-1/2" ruler by Fiskars with a rotary blade attached to it, looked kind-of like a paper-cutter, but it was meant for quilting! Wal-Mart carried it in the quilting section. I had to have it!
I was a young Mom with four little kids at home and had come home one day to a parent's worst nightmare. I pulled in the driveway behind a police car and emergency vehicle, several neighbors on the front lawn, and the babysitter crying on the stairs. My then four-year-old son had a blood-stained towel wrapped around his hand. He had gotten into my sewing cabinet and tried to use my "round scissors" to try and open a package that came in the mail, but got his wrist instead. The babysitter had called 9-1-1 and told them that he had cut his wrist with a knife. Traumatic.
Needless to say, I fell in love with a ruler that enclosed the rotary blade, and that children (or Mommy) would never be apt to slip and slice a finger or a wrist!!
It has a rubber strip under the right edge where the blade mounts, and you push it with the palm of your hand. It has 30o, 45o and 60o angles marked on it, and uses the same blade as any standard rotary cutter. The rubber strip holds it in place so the ruler NEVER slips, and I NEVER feel strain on my left arm (fingers, elbow, shoulder) just to hold the ruler in place while I cut. I have several of these for teaching young kids, and have only been able to find them at my local Wal-Mart, not even online. They may even be discontinued. If you come across one, grab it!
My other favorite is a new one by Eleanor Burns, her Quilt In A Day "Triangle Square-Up Ruler" This one saves so much time making half or quarter-square triangles. Students in my Carpenter's Star class last week finished sewing and squaring up all their blocks in our three-hour class. Most of them had time to also lay out their quilts and label the rows so they would be ready to sew when they got home. It is a lifesaver. Here is a link:
http://www.quiltinaday.com/shoponlin...ay.asp?i=23736
and you can see her YouTube demo of the 6-1/2" ruler here:
http://www.youtube.com/watch?v=5I-U_ZYcXH8