GPS.gov's directory of status reports and operational directories.
Navigation Center RSS Feeds for Local Notices to Mariners (LNMs) for each Coast Guard District. These feeds are update automatically as soon as we publish the latest LNM for each districts.
Currently monitored by Tripwire.
A site that keeps track of the statuses of various Tor network markets. No RSS, no API, can probably scrape it.
Daily reports about the global bgp routing table.
The Wikipedia page describing all of the known more-or-less standard HTTP status codes. Useful for people developing web applications.