Rule: Presidential candidates can only be current or former senators, governors, or representatives. (No “Limbaugh/Beck vs. Maher/Colbert” races.)
I think it would be hard to find a more polarizing election race than: Rick Santorum + Sarah Palin vs. Barbara Boxer + Elizabeth Warren
Or maybe: Ted Cruz + Ron Paul vs. Hillary Clinton + Nancy Pelosi
For the Pubs, I’d go with Todd Akin as the head and then either Bachmann or Palin as a running mate. On the left its a bit harder, because no matter who is chosen will be portrayed as the most Liberal candidate ever to be seen whose election will destroy America. But you could probably go with say Al Sharpton and maybe Keith Elison to bring out the anti-Muslim hysteria vote.
ETA: didn’t see the previously elected requirement. Replace Sharpton with Jesse Jackson Jr.
I just like the idea of Palin and Quayle both wearing shirts that say “I’m with stupid,” and arrows pointing at each other. Also, it’d be really funny if Sarah Palin punched Quayle in the stomach.
Boxer is relatively unknown. Warren, too. They’re not comparable to Pelosi; even the politically unaware know that Pelosi is (at least in right-wing narrative) the liberal-in-chief, and everyone knows who Hilary is (though I have never figured out why she is so unpopular). For a really polarizing race you need preexisting hate.
Pelosi + Eric Holder seems like it’d be the ultimate right-wing-hate ticket.
For the other side I’d go Gohmert + Steve King, but they are relatively unknown to the wider public too.