The new buzzword is "dark money." Since the US Supreme Court's decision to override Congress and allow unlimited secret cash from corporations (even from foreign governments) to influence US elections, following the money has gotten hard.

That was the effect of the January 21, 2010, Citizens United v. FEC case. Reporters trying to trace the effect of secret millions on the looming November 2, 2010, election can still get a little help from some old open-government allies.

One of the better sources of information on "independent" campaign spending is the Sunlight Foundation, an open-government nonprofit that works magic with online data. The Center for Responsive Politics (opensecrets.org) also offers help, however fragmentary.
 

• Check out Sunlight's "Follow the Unlimited Money" [2] searchable/browsable database.
• Sunlight offers other helpful resources on its site [3]. Just one example is the October 20 blog post by Ryan Sibley, "Dark Money: Super PACs Fueled By $97.5 Million That Can't Be Traced To Donors" [4].
• Also helpful is the Center for Responsive Politics site. [5] Check out their compilation of data on outside spending [6]. And their special section on the impact of oil money on elections. [7]