One of the guys at work showed me something called Packet Tracer (part of the Cisco Networking Academy packages). It's a bit similat to GNS3 but a lot more advanced (full visual view of device, more devices, less memory hog, drag-drop components, no IOS images needed,...). Unfortunately, it doesn't appear to be available for free.
Re:dynamips?
Beatnik on 2008-02-17T11:53:29
Well, GNS3 runs on top of Dynamips;)