Enter the following at the press start screen

unlock all characters exept Syn and Kron
L1, R2, R1 square, down, circle,down L2, square, square, sqaure, sqaure
Submitted by John C. Taylor

unlock Syn 

R2, right, R2, square,R1, down, R1, R2, R2 circle
Submitted by John C. Taylor

unlock Kron

L2, L2, up, up, up, left,down,up, circle, L1
Submitted by John C. Taylor 

Unlock Juni

Up, Left, Left, Up, Square

Unlock Khan

Up, Up, Down, Down, Triangle

Unlock Redempter

Up, Down, Left, Right, O

Unlock Stygian

Left, Right, Left, Right, T

New costom for orion 

R2, down, down, circle, sqaure, sqaure, R2