Ferro cable snake
This is perfect in it's simplicity. It's SOOO easy to install and perfectly suited to where you have an existing set-up and you don't want to turn your desk over to get your cabling sorted.
It grabs all your cables and tucks them up neatly under the desktop. We'd like to say it's special. It's not - it just does the job without any fuss.
Just stick it to the underside of your desk ( screw it in if you want) and run your cables along it.