At Macworld this year, I got a chance to try out the new SRS iWow 3D. It's an interesting little dongle that fits on your iPhone, iPad, or any iPod, including the touch, that has the 30 pin connector. When you connect it, plug in your headphones to it, and click the on button, it enhances the sound coming from your device in some interesting ways.
I have no idea what's behind the magic that this little device does. What I do know is that it seems to enhance the sound impressively. The stereo separation seems much greater. The highs brighter, and the bass deeper. Works great with music, but the enhancement when playing videos was even more dramatic.
SRS has also created an iWow 3D app that lets you tailor the sound to your preferences. You can set the output for different devices such as headphone or speakers, and you can increase the treble and base to your preferences.
If the sound is important to you, it may be worth carrying around an extra piece to you. You can pre-order the SRS iWow 3D now from SRS directly.