The 60 degree rulers I have seen are triangles, not diamonds but I'm sure I haven't seen every ruler that is made! OBW or one block wonders are made with this ruler. Do a search above and type in OBW and you will get many, many results
I typed in the search feature and this is a list of what I got:
http://www.quiltingboard.com/search.jsp?q=obw&u=