Five years ago Paul Rademacher reverse engineered Google Maps to put Craigslist homes and rentals on a map on his site. The site essentially pre-launched the map mashup category, because there was no Google Maps API at the time. Even now, Paul's HousingMaps.com is the prototypical example mashup and still used by many to find their new homes (and our HousingMaps profile is of course one of the first mashups added to our directory back in 2005). Since then, as we've seen, the Google Maps API has gone on to be the most popular API to use.
Google Maps Mania tracks the history, all the way back to a Craigslist discussion board posting. Originally the site ran off of Rademacher's website, but he purchased housingmaps.com a few days later.
Today Rademacher is a Google employee, hired not long after he created his trail-blazing site.
Things moved quickly in 2005. Adrian Holovaty, who later went on to found EveryBlock, created a Chicago transit map. A month later, Holovaty announced Chicago Crime, which embedded crime data in Google Maps.
ChicagoCrime.org, shown below, has since been retired, but it remains along with HouseMaps as one of the innovative applications that demonstrated the great potential for what mashups could become.
Finally, seeing all this innovation, Google officially launched its API in June 2005 (I covered the launch on my personal blog). ProgrammableWeb was started shortly thereafter and this site now lists over 2,000 mapping mashups.
Including the one that started it all.