WireShark 1.0

WireShark is a protocol analyzer based on pcap libraries and usually used to check nets and develop net applications.

When we use it we find a big versatility which makes it to support more than 480 different protocols, furthermore you'll be able to work with data captured during the same session or with stored data from the HD.

WireShark supports the tcpdump standard format and it can rebuild TCP sessions and its graphic interface is very intuitive.

Note:
It requires WinPcap.