I went through a lot of APIS when building DOOMcast. The one that really stands out is the USGS GeoJSON API. The feed is updated in real-time. Formatted well. Its excellent.

USGS follows the GeoJSON spec for geographic features. So if you’ve worked with this spec int he past it should be a qauick read.

USGS doucments the params you can pass here: http://earthquake.usgs.gov/fdsnws/event/1/

Earthquakes for the last 24 hours: http://earthquake.usgs.gov/earthquakes/feed/v1.0/summary/all_day.geojson

You can get more detail on an event by passing an id: http://earthquake.usgs.gov/fdsnws/event/1/query?eventid=hv60995496&format=geojson

From there you can get a list of cities close to the event: http://earthquake.usgs.gov/archive/product/nearby-cities/hv60995496/us/1438426393480/nearby-cities.json

Its a fun API. The best I’ve worked with in a while. Would really like to see USGS pass it on to GeoMAC Wildfire feed.