I have been having this problem for years and never got down to really fixing the problem. I can never really control the cables on my robots cortex especially since my team uses 12 motors, extension cords, sensors, a daisy chain of 4-wire cables and a power expander. If there are any tips to help me manage my cables that would be greatly appreciated!
We used to have this problem. What our teams have found that works is split flexible tubing. For most things, I think the size they use is 1/4 inch. For a few things, they use a bigger diameter. They bought some a couple of years ago. They bought a roll of two different sizes. Since the lengths are all standard lengths, they can reuse the parts they have cut.
After a lot of experimenting, they determined that it is best to not have the connections between wires and extensions inside to tubing. They also do not keep the fat part of the motor controller inside the tubing.
Using the tubing along with small zip ties keeps the wires looking nice and out of the way. For the connections, between the extensions they use VEX Extension Cable Retaining Clips. These are great for 2, 3, and even 4 wire cables.