Alameda County is hosting their first hackathon on 12/8/12. Using Alameda County datasets, Build, Design, Create, and Share new concepts and apps that will benefit citizens and improve civic engagement. There will be free food and prizes. The event is only 2 blocks from BART in Castro Valley. Register soon as time is running out. http://code.acgov.org
See http://data.acgov.org for a list of datasets that could inspire you.