Well, first thing to do is to keep all of your power cords away from the other audio and video cords. They can introduce a 60Hz hum into your system which is very annoying. If you must cross a power cord with some of your other wires, do so at a 90 degree angle. Speaker cables don't HAVE to separate from the others, but it can't hurt. As for actually keeping them organized, I've found that bulk velcro works very well. Grab 50ft or so and cut it to the lengths you need. Works great for computer setups too!
You might want to read this
article.
Ram Electronics sells that stuff as well. You might be able to find it locally.
