Expendicus, along with several other entries in the Apps For America contest, got a brief mention on the OpenSecrets Capitol Eye blog for making use of CRP/OpenSecrets data. Expendicus uses the OpenSecrets API to show top industry and organization contributions to specific candidates, as seen here for Rep Giffords. The contributions by industry set alone is a fantastic resource and the community owes a lot to CRP for all the work they do coding and maintaining this data.
The other major data source in Expendicus is independent expenditure data. This data takes the form of a source committee, a contribution date, contribution amount, a support / oppose flag, and the candidate whom the expenditure supports or opposes. CRP does make this data available on a per-committee bases ( DCCC) and per-race basis (MS-01) but this data wasn't available through their API.
To generate this data I created a ruby library to expose electronically filed Federal Election Commission reports in a uniform way across file formats and revisions. After some cleanup work the library will be released under the GNU license on the Offensive Politics page on github. In the mean time Expendicus allows you to download a CSV file of any of the independently generated data displayed on candidate, committee, or district pages. Alternatively you can download the entire Expendicus data set (includes independently generated committee, candidate and district financial summaries) or just the independent expenditure data for 2008.
Thanks again to OpenSecrets / CRP for all their hard work and contributions to the community.