Here's something I found that's no less than spectacular, it's headphone-specific, and for headphones whose sound falls within a more-or-less high fidelity range, the fixup is amazing. Most users assume you wouldn't change the soundstage or the 'constricted' effect with EQ, but it does work, and sometimes makes all the difference in the world.
http://rockgrotto.proboards.com/thread/9667/headphone-equalization-audioforge-app
http://rockgrotto.proboards.com/thread/9667/headphone-equalization-audioforge-app