Network discovery tools

I was wondering if anyone could recommend a good shareware or demo network discovery tool. I was hoping to find something that will show vendor type during node discovery. I came across a tool called network ferret that did the job, but nothing downloadable. I'm hoping to do some more work on the effects of network diversity, and wanted to do testing on real world networks. I figured starting of with GMU would get us going, but if anyone knows of any available datasets with node-link topology and vendor type it would be great to play with them. thanks, sean