The prevalence of mashups on the web is probably thanks to the Google Maps API as well as the 100+ other mapping APIs. It remains the most popular type of mashup, more than three times the second-most, photos. The ubiquity means maybe map mashups have lost some of their luster.
But things are changing. Twitter is geocoding tweets, location sharing is available to all. Now, maybe I'm biased, but I think 2010 is going to be a big year for location on the web. These three mashups may not blow your socks off, but they each have an element not seen in every map mashup.
Local Twitter Trends with Google and Yahoo: This application find local twitter trends for your city. Just click on the map, and the trends will appear. Also uses the Yahoo Term Extraction API. APIs: Google Maps, MaxMind GeoIP, Twitter, Yahoo Term Extraction. More at our Local Twitter Trends with Google and Yahoo profile.
Photospots: A place for amateur photographers to share their favourite photography locations. APIs: Flickr, GeoNames, Google Maps, Ordnance Survey OpenSpace. More at our Photospots profile.
geognos: Shows textual and visual information for all countries. For each country, a live map and photos are included, plus a map translated to your language. Uses Google Charts for data visualization. APIs: Google AJAX Language, Google App Engine, Google Maps, Google Visualization, Panoramio. More at our geognos profile.