DarkStat is a simple nTop like Packet Sniffing Network Traffic/Bandwidth monitoring utility for your Linux/Unix. DarkStat relies on libpcap and presents simple webinterface with nice graphs and stats aut-refreshed. The main advantage of Darkstat is that of the footprint and the memory, CPU usage.
DarkStat can run on most of the UNIX, Linux, FreeBSD,OpenBSD,NetBSD,Solaris,Mac OS. There are also packages for Gentoo Opensuse and Debian