There are a couple sites doing great work to expose corruption and criminality within US law enforcement. The vast majority of these crimes receive minimal attention from the regular media or citizens, and the criminals themselves (the officers) typically receive little or no punishment.
http://www.innocentdown.org/
Clyde Freeman and his innocent down project try to document the innocent victims killed by police abuse.
http://freedominourtime.blogspot.com/
Will Grigg continues to do some very good in-depth articles on cases of violent and/or lethal police abuse.
CopBlock.org
is a site encouraging citizens to learn and assert their rights, understand that badges to do grant extra rights or immunity from the law, and that filming the police is a critically important step we can take to keep these officers accountable.
http://www.huffingtonpost.com/news/the-agitator
Radley Balko has been active for years trying to bring cases of police abuse to the attention of everyone. His site The Agitator is now housed within the Huffington Post.