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, this program can scan hundreds computers per second. It simply pings each IP address to check if it's alive, then optionally it is resolving its hostname, scans ports, etc.
 
 

 
 
 
http://eusing.com/ipscan/free_ip_scanner.htm