Cable drops are little nubs of rubbery plastic that adhere to most surfaces and hold your cables, whether they're hanging off a desk, upside down or right-side up. Of course, if you need to remove them, you can pull them out and put them back with little effort.
I've been using cable drops for years, but we've failed to feature them on Lifehacker. You can get a similar hack with magnets and binder clips, which is great in some situations but easy to accidentally knock out of place in other situations. CableDrops stick to most surfaces and stay there.
You can position them underneath a disk to guide cables where you want them to go and prevent them from hanging down. You can also keep them on the side or top of your desk for easy access. CableDrops work very well, and they come in a variety of colours in packs of six (white, black, neon colours and muted colours) for around $US10 (some cost more, some less). It's not a bad price to get a few, try them out and see if they work for you.