The best rotary cutters are from OLFA. You can purchase them from JoAnn fabrics. They aren't cheap though.

They make several sizes, the smaller ones are better for cutting curves and the lager ones are better for straight stuff.

Be careful with these things, they are extremely sharp.

I bought my wife one for sewing years ago and saw how good a job it did. I was thinking I
better buy myself one, all that changed when I caught her cutting cardboard boxes with it...
It's mine now.