An internet petition to repeal FATCA has been underway for some time now: http://www.signon.org/sign/repeal-fatca?source=c.em.cp&r_by=188650
You can also write your Congressmen and Senators. Here is a link to an American Citizens Abroad page which includes a sample letter: http://www.aca.ch/joomla/index.php?option=com_content&task=view&id=466&Itemid=2
http://www.aca.ch/ (an international non-profit organisation that seeks to protect the rights of Americans abroad). They are a good bunch of people and do a great job for us, please join up and donate lots of money to them! They also have country contacts, so you might want to start a chapter in your country.
http://www.aaro.org/ (similar to ACA except AARO seems to concentrate more on Citizenship than on tax issues).
http://isaacbrocksociety.com/ (a site set up by Americans in Canada about double taxation, FATCA, FBAR, VDP, citizenship, renunciation and the like.) Lots of keen debate on this site!
http://www.hodgen.com (a tax attorney in California who has dealt with Voluntary Disclosure and FBAR problems.) A discussion of constitutionality on that blog may be found at http://hodgen.com/for-those-of-you-who-think-the-ovdi-penalties-are-unconstitutional/
Here is an interesting post that argues the unfairness of US policy as well as emphasizing that it is to the disadvantage of the US economy: http://renounceuscitizenship.wordpress.com/2012/01/12/u-s-citizenship-based-taxation-harms-u-s-economy/
FATCA Fallout — Mass Renunciations http://opiniojuris.org/2012/01/08/fatca-fallout-mass-renunciations/