You can find some data of mixed completeness/usefulness here[1]. Data.gov has gotten much better in terms of usability over the past few years, but it's still a crapshoot, and it's generally more effective to go directly to the agency/organization that you want data from/about. I think it's a great idea though, and I hope it's not the sort of thing that will get neglected or die if there's a party change at the White House level (although I suspect that could easily happen).

[1] http://catalog.data.gov/dataset?q=police&sort=score+desc%2C+...