Well I know NOTHING (quite literally) about making sigs and pics on GIMP or PS...
I know what looks good though and I think what you need is some color blending... maybe overlay but i could be totally wrong.
its to sharp on the edges unless that is what you were aiming for? and maybe add some more detail to the bacground another picture that has got lots of shading on it and blurring, or something like that or just another layer with a pattern on it that would go good with the one you already have.
but heh I know nothing about making pictures so...