ettercap 0.8

Access a set of libraries and tools to intercept, log, and analyze network traffic and data and prevent man-in-the-middle attacks. Generate reports showing security breaches inside the network. The solution works with a broad array of network protocols, including ciphered ones.

Ettercap is a suite for man in the middle attacks on LAN. It features sniffing of live connections, content filtering on the fly and many other interesting tricks.
It supports active and passive dissection of many protocols (even ciphered ones) and includes many feature for network and host analysis.