This is a very simple knot that my friend Brian showed me. It's fun to tie and has a wonderful elegant look to it. I used two colors of cord here to make it easy to see the steps. Here's the last two pics showing the tightening process:
You start with your cords side by side, make two loops and pass the ends through the loops. Then you pull them through a little ways and pass the ends through the next loop. Tighten the whole thing up gradually as you will have to twist and work the loops a little bit as you pull everything taut. After practicing a few times it will be a piece of cake.