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.
ManageEngine OpManager - Monitors routers, switches, firewalls, load-balancers, wireless LAN controllers, servers, VMs, printers, storage devices, and everything that has an IP and is connected to the network.
UptimeRobot - Free Website Uptime Monitoring
Cisco Data Center Network Manager - Cisco Data Center Network Manager offers network management system (NMS) support for traditional or multiple-tenant LAN and SAN fabrics.
Datadog - See metrics from all of your apps, tools & services in one place with Datadog's cloud monitoring as a service solution. Try it for free.
DCImanager - DCImanager is a platform for managing physical equipment. Connect any physical equipment to a single platform. Use the platform to manage your servers, switches, PDU as well as physical and virtual networks.