Honestly, I had a little trouble following the Wikipedia article about mashups; however, once I started exploring, it was a lot of fun!
Unless I am reading something wrong, the Mappr has changed. Flickr now has a way to place your photo uploads on a map...since I had already posted some photos on Flickr I used the opportunity to attach those photos to the location where they were taken (pretty cool stuff).
Of all the mashups, I enjoyed BigHugeLabs the most! I created a magazine cover, a puzzle, and a trading card. If you visit my Flickr site, you can see them all. I think that I could incorporate some of this into my classroom. It would be fun for the students to create trading cards that hightlight the computer skills they learn in my class...or create posters with their team names on them (I use lots of cooperative learning in my classes).