Angry IP Scanner
Angry IP Scanner is a small open source Java application which performs host discovery ("ping scan") and port scans. The old 2.x release was Windows-only, but the new 3.X series runs on Linux, Mac, or Windows as long as Java is installed. Version 3.X omits the vampire zebra logo. As with all connect()-based scanners, performance on Windows XP SP2 and newer be poor due to limitations added to tcpip.sys. The FAQ provides details and workarounds. A short review was posted to nmap-dev in 2008.
Superscan is a free Windows-only closed-source TCP/UDP port scanner by Foundstone (now part of McAfee). It includes a variety of additional networking tools such as ping, traceroute, HTTP HEAD, and whois. Some functionality has been crippled by restrictions imposed by Microsoft in Windows XP SP2 and newer releases. This tool is not really maintained (the latest release was in 2004)
NetScanTools is a collection of over 40 network utilities for Windows, designed with an easy user interface in mind. It includes DNS tools, a ping and port scanner, traceroute, and other utilities. It comes in bundles with more or fewer tools based on the price.
Unicornscan is an attempt at a User-land Distributed TCP/IP stack for information gathering and correlation. It is intended to provide a researcher a superior interface for introducing a stimulus into and measuring a response from a TCP/IP enabled device or network. Some of its features include asynchronous stateless TCP scanning with all variations of TCP flags, asynchronous stateless TCP banner grabbing, and active/passive remote OS, application, and component identification by analyzing responses. Like Scanrand, it isn't for the faint of heart.