I wouldn't bother with command line stuff - you'll need decent graphical stuff to get decent info.
The answer really depends on what you're trying to do. If you want SNMP-based traffic info, MRTG.
If you want top of the range end-to-end performance/traffic analysis, then Niksun NetVCR / Compuware Network Vantage or the like.
Basic stuff like Microsoft NetMon, Sniffer and similar tools will be a good start - plus they're cheaper !
If it's application troubleshooting, then stuff like OPNET's IT Guru would be the sort of thing you're after.
In essence, let us know exactly what you're trying to achieve and we might be able to target suggestions more.
And couldn't you tell I do this for a living !