eEye Digital Security. Best scanning tool is now on Windows
Sysinternals Freeware – Utilities for Windows NT and Windows 2000. A very nice set of utilities for Windows
Security Tools : ScannerAn easy place to fine the scanner stuff. Watch out for viruses in them though!
NetworkEval.COM Home PageAnother site with something that identifies all shares
SC Magazine. Of course there is a security trade publication!
Nmap — Free Stealth Port Scanner For Network Exploration & Security Audits. Runs on Linux/Windows/UNIX/Solaris/FreeBSD/OpenBSD. This appears to be the port scanner of choice.
Auditing Inside the Enterprise via Port Scanning & Related Tools. Here is a good list of software tools to get to do intranet scanning