Is there a good way to create a marker texture in photoshop.  For example, to make a photoshop render that ws used with traditional brushes (airbrush, etc), and put a texture over the top of it to look like it was drawn with markers? 

Best thing for that is Painter...

OR scan a texture that was done with either grey or black marker, then apply it as an Overlay. Soft Light, etc.

Hope this helps-

-Lew ;-)