for San Francisco, Salt Lake City, and Orange County, are now posted at EightMaps.com. Proposition 8, of course, was the proposition that amended the California Constitution to bar legal recognition of same-sex marriage. The map is built -- presumably automatically -- from the data reported by the California Secretary of State's office. (The site I linked to contains the committee id's, but if you click on the committee name, you'll see the individual contributors.) Many of the listed contributions are $50 or below.
I suspect this sort of technology may well make people much more reluctant to donate money to (or against) controversial propositions -- and may lead people to rethink whether the government should indeed mandate disclosure of such contributions, especially small contributions. In any case, I thought I'd note this.
I recognize that mentioning the site may exacerbate the problem that I describe, but it's also necessary for readers to understand what's going on. And the site has of course already gotten a good deal of attention from other places.
Finally, I should note that I think the organizers of the site have the First Amendment right to put it up, and I would oppose any attempts to outlaw such speech, or to make it civilly actionable. (For more on why even more dangerous speech should generally remain protected from government restriction, see here.) But the question is to what extent the government should make the creation of such maps easy, by making available information about ballot measure donors, including small donors.