This is a really interesting website: DoSomething.org
The thing that's neat about it (if you explore the site) is that you can pick an issue, pick how much time (as little as 1 minute), pick who you want to work with (alone, a group of friends or church, an organization), pick where and they will give you ideas. ex. Preventing Bullying, 1 minute, Alone, here - Make a poster and hang it in your library.
Lots of ideas at many levels of involvement, information about different causes with the understanding that there may be different legitimate viewpoints and levels of passion. Check it out!