every achievement/trophy unlocks a special cg in gallery mode
100% in story mode for a char unlocks a special jap interview w/ said char's VA

If you beat arcade mode with RAGNA you unlock UNLIMITED RAGNA.

The same should apply to HAKUMEN, RACHEL AND NU. If you beat the game on arcade mode with those you should unlock there UNLIMITED VERSIONS. to access them when there unlocked just press R1.

You also get CG's for not only going through the storymode scenes, but getting some of the arcade stuff down as well, like the ending cg's and whatnot. It's pretty cool, as some of the art has captions at the bottom by the artists telling you how they drew it or what they were thinking, etc. For instance, there was quite a debate over the size of Noel's breasts during character development....it's interesting. Though there's no really cool unlockable character stuff yet, though I'm hoping we get downloadable costumes or something.