According to Wikipedia, In technology, a mashup is a web application that combines data from more than one source into a single integrated tool; an example is the use of cartographic data from Google Maps to add location information to real-estate data from Craigslist, thereby creating a new and distinct web service that was not originally provided by either source.

Mashup originally referred to the practice in pop music (notably hip-hop) of producing a new song by mixing two or more existing pieces.

When I brought MashupAds.com back in 2006, I had a pretty good idea why the use of Mashups would be great in Advertising. Consider this! Any changes happening in the social, business, technological or personal aspect of our lives is first noticed by the masses by way of advertising and/or news. The key is to predict news before it becomes news.

MashupAds.com was purchased by Dapper inc. Dapper deals with different data sets across different web platforms and technologies. You may find the site useful.

On the net :

MashupAds.Com : Dapper.Net