Monarch Migration Explorer
See this map online at http://monarchs.johnbeales.com
This generates a Google Map of sightings of Monarch butterflies over the past six years.
In order to use it for yourself, rename creds-sample.js to creds.js and add a Google Map API key and a Flickr API key.
Everything is browser-based at the moment, so there's no need for server-side coding or even a webserver.