I find myself conflicted about many mashup sites I run across, mainly because they take the term "mashup" too literally, combining functions and visuals from different sites in a haphazard manner so that the aesthetics are horrendous and the usability is absolutely nil. And then I discovered Mashup Awards, a site dedicated to finding the "best mashups on the web." Judging criteria include: uniqueness, creativity, user experience, utility and content. Two award-winning sites I find rather fun and useful are BookTour and LazyLibrary. See below for screenshots.

BookTour is a mashup that aggregates information from Amazon, Google Maps and Google Earth along with information the users and authors enter to provide information on when authors are speaking and their works.



LazyLibrary is a mashup that pulls information from Amazon and filters out books greater than 200 pages. They quote Einstein to sum up their philosophy: "Everything should be made as simple as possible, but not simpler."