Map Mashups: the what and why and which APIs are popular

Interested in seeing which Mashup APIs are popular? This is the topic in this recent discussion post... interesting! This article from Apex devnet provides some insight on developing a mashup using the slaesforce.com platform... The second article in this series presents several concrete techniques for building mashups. By the end of the second article you will be in a position to comfortably create your own mashups on the Salesforce platform. The article looks closely at the Gogole maps API, using AJAX, and other APIs... http://wiki.apexdevnet.com/index.php/Mashups:_The_What_and_Why Of interest, some of the most popular APIs for mashups according to programmable web include:
Google maps 50%
Flickr 10%
YahooMaps! 4%
Virtual Earth 3%

Looking for data or tools for your mashup? Try some of the following:
Yahoo! Geocoding service - http://developer.yahoo.net/maps/rest/V1/geocode.html
USGS Geonames - http://www.geonames.org/export/
USGS Elevation Service - http://gisdata.usgs.gov/XMLWebServices/TNM_Elevation_Service.php

So what kind of mashup are HOT besides mapping? According to programmable web, video mashups, social mashups and photo mashups are leading the pack lately!