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.
PingInfoView - PingInfoView is a small utility that allows you to easily ping multiple host names and IP addresses, and watch the result in one table.
UptimeRobot - Free Website Uptime Monitoring
SmokePing - Smokeping is a tool for measuring latency.
StatusCake - Website Uptime Monitoring & Alerts – Free Unlimited Downtime Monitoring
PingPlotter - PingPlotter is a troubleshooting tool that helps IT professionals and neophytes identify, diagnose, and resolve network issues.