IP-Toolbox.com - IP-Toolbox.com is the best site for quick and easy viewing of your public IP address and other related information.
HostedScan.com - Online vulnerability scanner for servers, networks, and web applications.
GRC Port Scan - GRC Internet Security Port Scanner. Tests for open ports on your external IP address.
HackerTarget.com - Security Vulnerability Scanning based on Open Source Tools.
TrueIP - TrueIP is a small program that runs in the system tray, monitoring your IP address(es).
Intruder - Intruder is a security monitoring platform for internet-facing systems.