I can see equating Ron Paul and Dennis Kucinich. They are both kind o fringe politicians who have managed to get some level of success (both in congress) but neither of whom has a chance at the presidency. Obviously on the specific issues they are worlds apart, but they exist in the same kind of party space on opposite sides.

I'm having trouble thinking of a democratic equivalent to Alan Keyes. There are some damn nuts democrats (hello, Sharpton, I'm looking at yoooooouuuu....) but none I can think of that are treated nearly as seriously by the left as Keyes is treated by the right. I know, keyes is considered a joke on the right too but the GOP tried to run him as a senator for god's sake. That's a higher position than either Paul or Kucinich, and Keyes is way more insane.