Most any brand. My favorite are the Pachmayr. They grind pretty easily and they are available in a wide variety of thicknesses, patterns, and sizes. You go to their website, pick the style and thickness you want, look at their chart to get the model number that is closest to your buttstock end size (but still bigger to allow for grinding) and then order that model from whatever online merchant carries it. There is a good Larry Potterfield video on Youtube that shows you how to grind a pad. He uses big fixed disk sander and a fancy jig to hold it while grinding but you can do the same with home belt sander or sanding disk mounted on a drill.
