whatismyip.cc - External IP Address lookup tool with option to scan the external IP address.
Pingdom - With website monitoring from Pingdom you will be the first to know when your website is down. No installation required. 30-day free trial.
What is My IP Live - Find your IPv4 and IPv6 just by visiting whatismyip.live - complete IP geolocation is also provided along with some other useful IP tools.
StatusCake - Website Uptime Monitoring & Alerts – Free Unlimited Downtime Monitoring
GRC Port Scan - GRC Internet Security Port Scanner. Tests for open ports on your external IP address.
Better Uptime - We call you when your website goes down