The Independent Expenditures page of the California Fair Political Practices Commission is the site of the day

The Fair Political Practices Commission (FPPC) has placed a page with links to help ensure the public know which interests are funding political campaigns with “independent expenditures.”

Now you have one place to go to keep current on this information that may affect your vote and also be useful in writing articles and monitoring these burgeoning sums of money—where they are coming from and where they are going to.

The FPPC is providing a daily listing of independent expenditures made on behalf of candidates in open legislative districts with contested primaries (26 races in all) from January 1, 2008, through the primary election on June 3, 2008.

This page states:

“Groups that make independent expenditures, as well as the daily and cumulative totals of independent expenditures made to support or oppose candidates, and the names of contributors who gave $10,000 or more to each independent expenditure committee are listed.

“Information under "Total IEs Made Yesterday" reflects data from the prior day's report, including IEs made, amendments to previously filed reports and late filed reports. Information contained in the May 16, 2008, report includes all IEs made from January 1, 2008 through May 15, 2008. Updates to the names of contributors who gave $10,000 or more to each independent expenditure committee will take place Monday through Friday.

“Comprehensive information on all independent expenditures is available on the Secretary of State's website at www.sos.ca.gov."

There are links for Senate races, Assembly races, and independent expenditure committees and donors.