Sony's offering a massive pre-order pack alongside the game, given you order it between now and release from a supporting retailer. The pack includes the game's soundtrack, exclusive themes for both the PSP and PS3, a PSN avatar, a character skin, and an exclusive game director's commentary. That's a ton of stuff.
Sony's also confirmed that the previously announced PSP hardware bundle is also up for pre-order at participating retailers. The pack nets you a black and red PSP, a copy of Ghost Of Sparta, a download code for Chains Of Olympus, a UMD copy of Kick-Ass and a 2GB memory stick.