I would recommend the June Taylor Shape Cut Ruler. Others have recommended it also, I see, but I want to re-recommend it. I could not possible cut straight strips without it. I did have to be shown how to fold the fabric before I understood how to use it, but once I learned that, I would not turn back. I cut with confidence now, and I did not before. I am fairly new to quilting thought, so that may make a difference in that I don't have years and years experience with another method of cutting strips.
Dina