Nast (Network Analyzer Sniffer Tool) is a great Packet Analyzer that is based on Libnet and Libpcap. . Although the creators of Nast are in period of silence, what they have created thus is usable and gets the job done. It sniffs in promiscuos and normal mode for packets on your network and then logs its results. Known Bugs - Port scanner and Promiscuous mode may generate incorrect results.
Nast comes with a few cool features:
Custom report Logging
Resets established connections
Catch daemon banner of LAN nodes
Capable of locating LAN internet gatways
Byte counting with optional filter
The current version for download is Nast 0.20 (nast.berlios.de). The previous version 0.17e suffices as well because of it's major bugfixes. For those afraid of the "latest version" stepping back to 0.17e wouldn't be a bad idea.