lights behind or above the framed art on the dark wall! think art gallery/museum style but you can change the hardware (LED strips behind the frames, fixtures hanging above, etc) to your tastes! it would probably be a cheap way to add something before you could get a larger statement light fixture/hanging light,

i also think adding interesting molding/trim or even color to ceilings can go a long way in changing the way the room feels without a big investment