Many of my fabrics are those I made but will go back and add "more" interest to the surface. One of my favorite stamps/stencils is the material below, found at construction sites and used when laying tiles. It gives the most interesting effect (see above, lower left corner).
And screening which is fun to use for overlays and also tones down areas of color.
Gauze is another great choice; it works like a transparent fabric. I like to pull threads from different areas and leave long threads. It's great for overlays.