The longest-running such seems to be, "Dems are tax-and-spend liberals". The easiest counter is to note that "tax-and-spend" makes a lot more sense than "borrow-and-spend", which is the Republicans' budget philosophy.
Still another response is the Steve Greenberg cartoon comparing "Fiscal Conservative" results with "Tax and Spend Liberal" results. [The previous link to this is now dead, but you can view it at Blog: Steve Greenberg's Cartoons ... scroll down!)
The most recent calumny is "the evil of Single-Party Rule": if Obama wins, the Dems will control the Executive and both Houses of Congress - ooh! Scary!!!
How to respond? The ideas below aren't well-formulated, but may provide a beginning.
1. Note that it was Republican control of the Executive & both Houses of Congress that got us into our current mess... and that it just might take Dem control to get us out!!!Again, these points are not well-articulated, but I believe they provide a basis on which to construct more convincing arguments to counter the "Single Party Rule"-is-bad Republican talking point.
2. (related to #1) We're facing a lot of very serious crises right now - economic meltdown, bogged down in two possibly unwinnable wars, America's international reputation in shambles.
Now is NOT the time to dither. We need deliberate, consistent policies enacted NOW to get us out of the hole W and his minions have dug us into.
(Maybe when we're out of the hole it would be appropriate to return to so-called "divided government"... but NOT NOW!)
Have a nice day.