Bandwidth Utilisation

My favorite tool, provided you have SNMP running on the target devices, is MRTG. This is a Web-based tool that runs on either NT or Linux and provides marvelous graphs of current and historical data.

MRTG is also free, and that makes it even better.

The best tool I know of is Network Associates Sniffer Pro.

www.sniffer.com

It will show all kinds of details on your network traffic and utilization with a simple dashboard type interface. You can evaluate errors, do packet analysis, everything. It will break down you utilization over time, show the types of packets, any errors, the systems using the most bandwidth...it'll even generate reports with nice colored pie charts or graphs (since that is what will usually have the biggest impact on management). ;)

Out of all the tools I use, its the one I'd never want to be without. That said...it's pretty expensive.

Have a look at Bandwidth Monitor by Idyle software. I've been using for about a year now & it works great. You can download a fully fuctional 30 day trial version. Has loads of features, daily weekly monthly as well you can have all your stats savedto a log.

http://www.idyle.com/software/internet/index.html