Where is a list of PACs and 527s - educate me please...

[sfwriter]

What organizations would you include in a survey of leading political think tanks, 527s, PACs, online communities and other organizations?

I'm producing a survey of the existing landscape.

I want a wide spread of examples from Democratic Underground to Free Republic and from Newsmax to the Nation and from The American Issues Project to the American Leadership Project and everything between. Think tanks like Heritage and Cato should be on there as well as left leaning think tanks and far right organizations like the NRA.

I’m looking to produce a survey of who is trying to influence the American public and how. What are the methods and tools being employed at Moveon.org and at Real Clear Politics for example?

Any suggestions and sources of research are much appreciated.