Network Monitor 3 free
Upcoming Network Monitor 3 will offer several new features and will finally be an uncapped, free, stand-alone application for Windows XP/2003/Vista/codename Longhorn (both 32 and 64bits):
- Real time capture and display of frames
- Simultaneous capture on multiple network adapters
- Multiple simultaneous capture sessions
- Network conversations and a tree view displaying frames by conversation
- Enhanced capture/display filtering (with intelli-sense)
- A new script-based protocol parser language, and script-based parsers
Source