Aerospace Composites offers a great product- vinyl coated kevlar cord. I use .038 (.058 also available) for pull pull in my 12 lb planes w/ no problem - and after crimpling / knotting or whatever to secure the end, a little heat will fuse the vinyl jacket and prevent it from loosening.

(URL below for Kev_Cord description)
http://www.acp-composites.com/acp-cord.htm