Plain old American Maple, 1/4" thick. You can purchase from any shop that caters to butchers. Works better than all the cones, iso bearings and Black Diamond shelving I have tried. I exlusivley use 1/4" Maple under everything. You should perhaps consider trying it as it is far less costly than some of the other options and I have found it to be far superior in sound quality. Now I will say that the Sony SCD-1 that owned at one time sounded best on the Maple supported by a tio of Walker Audio cones (the ultimate set). But everything else liked the plain Maple.
Mike
Mike