There are lots of great Internet resources tracking U.S. campaign contributions from individuals, corporations and industry and lobby groups. How ever you may have to do further research to show how these contributions have influenced policy decisions (as they almost always do.)
Federal Elections Commission
FECInfo Created by a former FEC employee, this site uses the Federal Election Commission's campaign contribution data, but presents it in a easy-to-use, searchable format.
Center for Responsive Politics
The Coin-Operated Congress are recent articles from the Mother Jones magazine, and searchable index of the 400 largest political donors. Searchable by name, industry, state and city. Profiles of the top contributors are also available.
Public Policy and the Corporate Agenda
If you haven't yet, search CorpWatch for articles that expose corporate influence over governmental institutions. Also check out our Money and Politics section in the Issue Library.
Check out trade association websites:
Learn about conservative policy think tanks, like the Heritage Foundation.
Monitor corporate influence in the U.S. legislature by searching THOMAS, which includes full text access to bills under consideration in the House of Representatives and the Senate, as well as the Congressional Record. The THOMAS Frequently Asked Questions list is a good "how-to" on searching legislation and other congressional information.