system
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There are more than 2 actually. But AdBlock is the best. 
Download page:
http://chromeadblock.com/
Changelog:
http://code.google.com/p/adblockforchrome/wiki/Changelog
FAQ:
http://code.google.com/p/adblockforchrome/wiki/FrequentlyAskedQuestions
Taken from the FAQ page:
Are you the same guys that made Adblock Plus for Firefox?
No, the main developer for ABP is Vladimir Palant and he lives in Germany. The main dev for AdBlock is Michael Gundlach and he lives in Georgia in the US. Both extensions use the EasyList filter list (as well as several others) and those are maintained by independent users.
Can I import my filters from Adblock Plus for Firefox?
Yes, you can. Select the rules in ABP in FF, press Ctrl-C, go to AdBlock options, Customize tab, click Edit, and paste them in that text box.