Dean's World has a post that's an excellent start on the many steps that could be taken to remove fraud from elections.
The trouble is: many machine politics cities (Chicago, Philly, Cleveland, etc.) don't want to get the fraud out. They just want the OTHER side not to be able to cheat.
I think I've figured out why the Dems are so sure that Republicans are cheating. It's similar to how adulterers think. They reason: I know I'm cheating, so I'll bet - no, I'm SURE that the other guys are, too. It is inconceivable that someone could have the opportunity to cheat, but have a moral code that they adhere to that prevents them from doing so.