From The Atlantic Cities:
Today, most major cities now offer some form of an online data catalog. You can find them at datasf.org or data.seattle.gov or data.cityofchicago.org. They contain both handy maps for novices (including, say, the locations of every bike rack in downtown Seattle) and sortable raw data sets for enterprising developers who can turn all these spreadsheets into smart-phone applications.
Non-profit initiatives like Civic Commons are meanwhile partnering with cities to convert valuable data into even more useful urban solutions like bus-tracking systems.