While not quite as pretty as BSOD or Walrus, NetGrok can show you real-time and historical packet data on your network (YouTube Demo).
You define a set of local nodes that are shown in a force-directed layout at the center, and any external nodes are shown in a hash-based layout. Nodes are sized by the number of connections and colored by their bandwidth usage. The sizes and colors are updated dynamically, and you can filter based on activity during specific time periods. External nodes can be manually grouped together, e.g., all the Google servers placed adjacent. Here's an example:
There's also an alternate space-filling treemap visualization:
Disclosure: I am one of the original developers.