Number 1: Is that an eSATA connection going to the back of your case? Do you expect you will ever use it? If not, I'd rip that out in a heartbeat and get rid of that extra cabling
Number 2: Try to tuck in that cpu fan power cable behind the mobo if you can at the top of the motherboard.
Number 3: Anyway you can reroute that black cable from the middle of your case over the top, and bring it in under your video card and then bring the connector through a gap between the video card and the case at the back.
Number 4: What is that red cable coming out over your power supply at the bottom and out the back of your case?
Finally, perhaps wrap some black electrical tape around that braided and striped power supply leads to make it less noticeable and let the cables blend in more with the black in your case. This is kinda a mind trick....but it gives the appearance of cleaner cabling. The same applies to the power lead going to the top case fan too. If you can darken down the color, you won't see the cable.