This dress created by YouTube user safirecat may not have been that difficult to create but the idea is still quite cool. It’s just EL Wire hooked up to a sound driver that changes the brightness of the EL wire on and off depending on the ambient sound levels. You can get the components from Cool Neon Lighting:
On a related note mentioned in the comments of the YouTube Video is this cool little project by Sensebridge called the Sound Spark its a pendant/necklace that reacts to ambient sound with flashing LED lights.
The Sound Spark is only $29 and comes with in 3 different coloured LEDs and two different necklace styles.
To go on another tangent, Sensebridge also sell the “Heart Spark” which does the same as the Sound Spark but instead gets it’s signals from a wireless heart-rate monitor (Sold Separately), I’m in no way affiliated with these people but I think what they sell is quite cool, they apparently are working on a product called the Mood Spark which is like a mood ring but it actually lights up in different colours. That’s pretty nifty, you’ll have to hunt it out on their website because I can’t be bothered linking to it (it’s not hard to find) apparently they have working prototypes…