Sampling the Web's Best Mash-Ups is weighted a bit heavily toward mapping, but still shows off what can be done when data is made available to the devil's playground. These idle hands are essentially free R&D... not a bad payback for an API.

"A raft of new Internet sites and services is borrowing from hip-hop culture's mash-ups, which combine two tunes to produce an entirely new song. Likewise, hackers are combining the data and features of two or more Web sites, creating entirely new, independent Web mash-ups that in the best cases transcend either of their forebears."