#1 Ntop

If you want to have a look at your data traffic flows, Ntop will take NetFlow or sFlow (both are network protocols to collect IP traffic information) data from popular switches and routers and display it in a Web GUI, complete with clickable links that take you to details about particular hosts or protocols or to actual conversations and flows.

There are interesting features to Ntop's output, such as identifying workstation users by their email addresses and (passively) detecting the operating systems of network hosts through packet analysis. Ntop will break down traffic volume on a per-protocol basis, helpful for comparing the traffic your network actually has to what you think it should have.

Ntop can give you a list of IP protocols, sortable by protocol type, as well as lists of traffic sources and destinations. Ntop also creates a matrix table of IP traffic, so you can see who is talking to whom and how much data is being passed between the two.

Also Read: 10 Best Alternatives to Google Reader and 5 Best Portable Networking Tools