Port Scanners:

Free IP scanner is a very fast IP scanner and port scanner. It is intended for both system administrators and general users to monitor and manage their networks. Powered with multi-thread scan technology, it can scan hundreds computers per second. It simply pings each IP address to check if it's alive, determines hostname, MAC address, NetBIOS information, scans ports, etc. The information obtained can be exported into a file as plain text file.

Also try Free Port Scanner 2.5 or Advanced Port Scanner 1.3