NetworkActiv Port Scanner 4.0
NetworkActiv Port Scanner is a freeware, fast, easy to use, advanced network scanner that can scan ports, IPs, protocols, perform DNS-dig, Whois, TCP/IP stack fingerprinting, trace-route, ping, and more.
It includes a skinable user interface and different operating modes to accomodate not only advanced users, but also network novices. This program comes with SYN (and UDP) based scanning engines that will always outperform any Windows based multi-threaded scanner. A multi-threaded engine is also included in case your system doesn't support SYN.