Outage Analyser is a free website that compiles data from 150,000 Compuware Application Performance Management agents deployed at customer sites. This is an interesting administrator tool because it attempts to show the root cause of an internet service outage, regions that may be affected, dependent services and detected down websites.
Each service provider has its own service status page (Amazon AWS, Google Apps health dashboard, Microsoft Azure Status Dashboard, Salesforce.com system status, etc). Outage Analyser is a neutral third party which attempts to aggregate most of that data (and more) and show it in an unbiased map.
I think Outage Analyser is a great tool for administrators but could definitely use a nicer interface.
The downside of Outage Analyser is that it only uses data collected from its customers therefore if its customers aren't using a service, an outage may not show-up.
This is a nice tool to keep in your toolkit but because of the limitations, can't be your only source.