A variety of people have requested information on how to track campaign spending. Here are a few of my personal favorites. I would love to hear if you have others to suggest.
Center for Responsive Politics
My all-time favorite tracking tool for campaign spending is
OpenSecrets.org, run by the Center for Responsive Politics.
Their search engine could use some work, but the information is generally there for those willing to dig a little deeper.
Here are some of the things that you can find.
Influence Explorer is a great tool courtesy of the
Sunlight Foundation. It doesn't provide as much detail as OpenSecrets.org, but it's a great starting point to see overall spending and relationships.
MAPLight.org
Influence Tracker
Influence Tracker is a fun tool courtesy of Wired Magazine, MAPLight, and OpenSecrets.org. Enter the name of a federal-level politician, last name first. It then creates a web page showing the contributions to the politician and (my personal favorite), a NASCAR-like shirt with the logos of the largest contributors.
The text box in the lower left corner includes code so that you can embed the result in your own website. Here's an example screen capture for Harry Reid, who is running for U.S. Senate in Nevada.

Don't confuse Influence Tracker with Influence Explorer listed above.
National Institute on Money in State Politics
FollowTheMoney.org is another good site that is very complementary to OpenSecrets.org, which focuses primarily on national races.
CampaignMoney.com
I find the
CampaignMoney.com site itself difficult, but it often comes up during Google searches. It only shows contributions to a campaign, and not spending with a PAC or a 527 committee.
I find it easiest to enter a search string directly in the browser address field. For example, here is a search for George Soros spending during the current election cycle. This gives you the general pattern.
ElectionTrack.com
ElectionTrack.com is a great resource for tracking campaign spending in California. It's fairly simplistic, but timely and easy.
Federal Election Commission (FEC)
California Secretary of State
FundRace
The Huffington Post
FundRace tool is another tracking tool for campaign donations. It has some relatively good top-level tracking tools on where money is going by occupation and city.
NPR
Here's an oldie but goodie from NPR dated from 2008. NPR has had some good journalism about "shadow money" (examples
here and
here), but I do have some concerns about possible corrupting influence going forward due to the
Soros/Open Society Foundation investment.