I like to farm in Nagrand at the Stonemaul Ruins (I think?) in the Eastern part of the zone. Essentially where the ogres are :) They drop runecloth and netherweave in decent amounts, plus you get kurenei rep every kill and also warbeads that can be turned in for kurenei or consortium rep. Good stuff all around.
Best spot to farm runecloth alone would be Tyr's Hand in Eastern Plaguelands. Netherweave alone, I would assume any 66+ mob has the highest drop rate, but you can just search it to check.
Note: See the search bar to the left? Make it your friend :) You could have searched for runecloth and gotten a breakdown of every mob in the game that drops it, just farm the one with the highest rate.