The Association of Community Organizations for Reform Now ("ACORN"), a far-left organization that engages in "direct action" such as (illegal) squatting campaigns and which is linked to Barack Obama. Their employees have frequently engaged in voting registration fraud, with hacks trying to claim that ACORN is itself as much a victim of that fraud as everyone else. During 2008, the Obama campaign hired them to do work in Ohio, and they also did GOTV efforts which redounded greatly to Obama's benefit. Obama initially denied on his website that he'd been an ACORN trainer, and then silently changed the site after the truth came out. They also support illegal immigration, even joining with Citibank to give home loans to illegal aliens.
DTN (lists past voting registration irregularities)