Subscribe via e-mail: 
WildPackets Omnipeek Personal is a free network monitoring tool for personal use. The .Net 2.0 tool has many features which most free packet sniffers/packet analyzers lack, especially when it comes to statistical analysis and visualization. Omnipeek is even better than Ethereal/Wireshark.
However, the personal version of Omnipeek has two limitations compared to the commercial version. It only supports one network interface and has a 25 node limit on Flows. Flows are conversations between two nodes (devices having a network address). Basically, this means that you need the commercial version to analyze the network traffic of a bigger network.
Toms Networking has a lengthy review with many screenshots about Omnipeek Personal.
I know you posted this a while ago. Looks like OmniPeek Personal is no longer available. And you can’t get to the trial download without submitting your Rolodex (well, not _quite_ that bad). They’re selling OmniPeek Basic (the most limited edition, not as in Rolls Royce Limited Edition) for about $1200!? Think I’ll stick with Wireshark.