There were a lot of cool mash ups and some really weird ones. These three were my favorites:
http://www.mapulator.com/
This is a map up that combines Goggle maps and network utilities such as traceroute and whois. It was really interesting to get a visual of how the web works by seeing it on a map. Sometimes it doesn't work because the computer doesn't get all or any of the locations.
http://www.wikimapia.org/
This is a site that combines with Google maps that lets anyone without being registured or anything to make little books that when clicked on give a description of the site or building. I liked it a lot. Most of the time it is a definition straight from Wikipedia but sometimes it's just people that let the world know "this is my house."
http://www.sergeychernyshev.com/maps.html
This map up simply puts Google maps right along side Yahoo maps. You really get to see differences in the two maps and especially in the satellites see which is more up to date. You also quickly realize that Google's is way better.
It also shows a very distinct difference between the two imagery machines in the views of New Orleans before and after Katrina from the looks of it. I think that Google had the post-Katria pictures but I'm not sure. I read in the Chronicle that they took them off the web for a while because they weren't up to Google's standards of picture quality but it seems they put them back up.
