Dejavu Technologies recently released TrafficScape, an appliance that grabs network packets and converts them into XML documents, which are then pulled into a database that is searchable through a simple, Google-like toolbar.
Have you tried to visualize your traffic flows? Did you have the problem that your graphs got really cluttered? Did you find a way around that problem? Did you filter data? Did you aggregate multiple nodes into one?
Do you know how much traffic is transmitted on your networks? Do you know what protocols are in use and what machines are using them? Are there spyware infected machines on your network that leak information?