There is another group of knots called "sinnets" that are loops over loops, or slip knots over slip knots. The benefit of this style of knot is that if you need the cord there is no untying, you simply pull the two strands and the whole thing pulls apart.
Cobra knot bracelet on the left, Ripcord Sinnet on the right
My favorite variation is the "Ripcord Sinnet", also called the "Zombie Apocalypse Bracelet" on some sites. It's very easy to make. If you can tie a slip knot you can tie a Ripcord Sinnet bracelet.
You tie a slip knot in the middle of 8 feet of 550 cord. Leave a little loop, it'll be the hoop that you use to close the bracelet. Flip it over so the loop is on the bottom, tie two slip knots on either side of the original knot. Loop one over the other, pull it tight. Tie another slip knot, loop it over the other and pull it tight. Repeat many times. (It sounds a little confusing but there is a very good video link at the bottom)
If you ever need to use the cord, pull on the two ends and it pulls apart into two strings of slip knots. Pull a little more and you have 8 feet of straight cord. Very cool.
I was going to make a video for this, but the gentleman at Fusion Knots does such a excellent job that I figured I would just post his video here.
I highly recommend the site Fusion Knots (http://www.fusionknots.com/index.php) for anyone interesting in 550 cord knot tying, for survival uses or otherwise. This guy has some very cool knots and explains them in a very simple, straight forward way.
550 cord is an incredibly useful survival tool and you never know when having the "Zombie Apocalypse Bracelet" might come in handy.