In Defense of Animals run by veterinarian Dr. Elliot Katz is the best organization I've come across. He's so dedicated to animal welfare. Sends informative literature, how the money is spent, etc. They accomplish a lot of good things.
http://www.idausa.org/index.shtml
Animal abuse will never end obviously just because some people are just messed up in the head. But at least, it can be exposed for the world to see and know about, and surely make things somewhat better.