WinPcap

WinPcap is state of the art software for Windows environments: it allows applications to capture and transmit network packets bypassing the protocol stack, it also has additional useful features which includes kernel-level packet filtering, a network statistics engine and support for remote packet capture.

WinPcap is Freeware, it is released under the BSD open source licence. Programmers have total freedom to alter and use it with their applications, even if it’s commercial. The binary and source code are available in the website.
WinPcap comprises all the classic relevant technology that is usually included in the packet capture literature. Besides, it comes with original features such as JIT filter compilation and kernel-level statistic processing. And this is the reason why WinPcap is, according to its manufacturer, better than other approaches.
WinPcap is used by many applications, both commercial as freeware: protocol analyzers, network monitors, network intrusion detection systems, sniffers, traffic generators, network testers, etc. Some of them, like Wireshark, Nmap, Snort, WinDump, ntop are very well known for the professionals in the area. Also, according to its manufacturer, WinPcap is downloaded thousands of times every day.
WinPcap has been revised and tested by many users over the years. Its programmers are seasoned Windows driver programmers which have a tendency for creating stable applications.
To sum up, WinPcap is good, reliable, has been tested, has commercial and free support, and what is better: WinPcap gets the job done!