PBS Frontline has a pretty good show on money in politics post-Citizens United, specifically in the state of Montana, that everyone should watch: Big Sky, Big Money. You should especially watch it if you don't know what a 501(c)4 is, or if you think SuperPACs aren't coordinating directly with campaigns. I have to say that I was hoping for a bit more dirt, or something more explosive, but honestly, Stephen Colbert pretty much nailed it months ago with his SuperPAC shenanigans. They obviously coordinate with campaigns. At least they have to name their donors. Non-profit non-campaign "issue advocacy" 501(c)4s don't, however. Except in Montana they not only coordinate with campaigns, they straight up run them.
As far as I know, only one supreme court justice (Thomas) believes that even anonymous corporate and individual speech is protected by the first amendment. So this is something we could actually win. But it's not like the Supreme Court is going to up and say "hey we screwed up, everyone has to disclose where the money comes from"--the legislature has to do that, specifically by passing the DISCLOSE act. Then Jim Bopp can challenge it and lose.
Also, given the current situation, where money wins elections, until we get public funding of campaigns, small donors are the only thing we've got. So donate to Jon Tester.