These images been around the web before, but I just rediscovered some examples of both good server room cabling, and bad datacenter cabling.
Data center cabling is really an art. It takes some time to get the network, power,and other cabling organized but worth it in the end. The benefits are more than aesthetic, good cabling improves airflow, cooling, and reduces problems with plug dropouts. Not to mention that good labeling helps in troubleshooting when an issue does arrive.
And The Ugly
More examples of good/bad wiring: