Federal court decisions, Citizens United and SpeechNow.org, opened the door for political organizations to spend huge sums on advertising explicitly supporting or opposing candidates for office. According to the Center for Responsive Politics, the Federal Elections Commission has so far authorized 33 "independent expenditure-only (IE) committees" that are legally allowed to raise unlimited funds from individuals, corporations, unions and other groups. CRP has been tracking the proliferation these so-called super PACs which advocate from both sides of the political spectrum. You can see the complete list here.
You can also browse the latest campaign spending of all IE groups with a searchable database created by the government watchdog The Sunlight Foundation. The data is sortable by committee, candidate and race. To date independent expenditures total some $57 million in the 2010 federal election cycle.
California races targeted by IE groups include the U.S. Senate and House districts 3, 10, 11, 19, 32, 36, 44, 45 and 47. Barbara Boxer's candidacy, for example, attracted $57,614 in IE funds ($3,484 in support; $54,130 in opposition). Carly Fiorina, in contrast, prompted $274,065 in independent spending ($235,362 in support; $38,703 in opposition). Boxer's biggest IE supporter is NARAL Pro Choice America. Fiorina's biggest is the Susan B. Anthony List, a pro-life political organization.