Built on GNU Public License, the open source Safari AdBlock was written with help from the folks who created AdBlock Plus, the popular Firefox plug-in. This iteration for Safari is simple and needs no configuration, although there are a few options for users if they want them. You can choose from blocking ads in a multitude of languages including English, German, French, Ukranian, Russian, Korean, Chinese, and more. That's about it for customization.
In my extremely scientific testing, where by "scientific" I mean utterly and shamelessly empirical, I checked out a few Web sites with big ads including CNN.com, NYTimes.com, and TheOnion.com, and AdBlock successfully killed ads on all three of them. Until now, the best way to block ads in Safari has been pay-for-play options. But for free and open-source goodness, Safari AdBlock is the way to go.