Enik Rising (h/t: Voir Dire) links to a PEW survey ranking votes' perceptions of the ideological position of various candidate. They came up with this chart
(click to enlarge)
What's fascinating (to me anyways) is that voters rate the Democratic candidates in the exact opposite order that I'd put them, liberal-to-conservative. The polls has the ordering (from most to least liberal) as Bill Clinton, Hillary Clinton, Al Gore, Barack Obama, John Edwards. I'm not trying to be snide here--I genuinely would rank the exact opposite: Edwards as the most liberal, then Obama, Gore, Hillary, and finally Bill as the most conservative.
The Republican ordering, by contrast, strikes me as about right: their order (from most to least conservative) is George W. Bush, Newt Gingrich, Mitt Romney, John McCain, Rudy Giuliani.
Why is the Democratic field perceived in a mirror-image to how I view them? I think a great deal of it is that John Edwards is a southern Democrat, and thus is kind of assumed to represent the more moderate wing of the party. I hear his accent, and even I have difficulty imagining him as a lefty. But of all the candidates, Edwards is the one most likely to be found breathing some progressive fire. Meanwhile, Bill Clinton was the patron saint of the DLC and the king of triangulation, so it's tough to call him the most liberal Democrat out there today (and Hillary has specifically gained accolades for being a pretty middle-of-the-road Senator). But him and Hillary both have faced a long, long effort by the right-wing media to tar them as pseudo-communists. Clearly, some of it stuck.
In any event, this raises interesting questions. Folks have worried about whether Hillary Clinton can ever shake the "liberal" label, no matter how centrist she runs. But what about Edwards? The same (but opposite) logic would seem to apply--he can apparently take relatively progressive positions while still being perceived as a moderate candidate. That could be of great use in the general. Of course, whether or not he will be able to avoid the liberal-brush of right-wing attack that is sure to befall the Democratic candidate remains to be seen. But still, it's worth considering.