Nmap - Nmap Free Security Scanner, Port Scanner, & Network Exploration Tool. Download open source software for Linux, Windows, UNIX, FreeBSD, etc.

whatismyip.cc - External IP Address lookup tool with option to scan the external IP address.

Angry IP Scanner - Open-source and cross-platform network scanner designed to be fast and simple to use

GRC Port Scan - GRC Internet Security Port Scanner. Tests for open ports on your external IP address.

Advanced IP Scanner - Advanced IP Scanner shows all network devices, gives you access to shared folders, and can even remotely switch computers off. Download it Free.

IP-Toolbox.com - IP-Toolbox.com is the best site for quick and easy viewing of your public IP address and other related information.