I wasn't familiar with the term "mashup" before, but have used these sites frequently. It is two different web applications mashed together to form one. There are so many different mashups and 3rd party apps out there to explore and use! One that I think is beneficial is Trip Planner. This site combines applications from Yahoo! Travel and Flickr to provide the user a way to plan trips. One can plan a trip, keep a journal about the trip, and upload pictures using Flickr. It can be shared and viewed by all. I would have liked to use this for the last trip my husband and I went on vacation. This could be a tool used in the library in collaboration with teaching a geography project with classroom teachers.