At least according to GovTrack, yet another of the many sources that rank where various politicians fall on the political spectrum. GovTrack seems to be unique however, in that it's rankings are generated not by how the Senator or Representative votes, but on the legislation that they have cosponsored. From the site, "The political spectrum image is generated through a statistical analysis of the cosponsorship of bills in the 109th and 110th sessions of Congress. The analysis places representatives who cosponsor similar legislation closer together --- it does not rely on party affiliation information or any analysis of bill content."
And according to them, Clinton is one of the most liberal Senators in congress. Here's a link to her specific site: http://www.govtrack.us/...
The "Radical" part of the ranking at first gave me pause, but they also call very conservative Senators and Reps. "radical" so it's not a partisan slur. Obama gets ranked by this site as more conservative then Clinton. They call him a "rank-and-file Democrat"
http://www.govtrack.us/...
They provides a graph showing where all 100 Senators and 430 odd Representatives rank. It seems fairly accurate. Collins, Specter, Snowe and Shays are ranked as the most liberal Republicans, which is basically true. Durbin, Lautenber, Kennedy and Boxer are rated as the most liberal Democrats. Which is also fairly where you would expect them. Reed (often considered one of the most liberal Senators) is ranked more conservativley, possibly because he is less active then most and probably hasn't sponsored or cosponsored that much legislation. Inhofe, DeMint and Chambliss are considered the most conservative Republicans. Again, nothing out of line there.
Clinton is placed as about the 5th most liberal Senator, behind the before mentioned Durbin group. There are a good 10 other Senators between Clinton and Obama, which could most likely be better explained not as "Obama is fairly moderate" but by the fact that he only has 2.5 years in the Senate, and thus has less ability to present Bills. Very liberal Whitehouse is ranked moderately here for the same reason.
http://www.govtrack.us/...
If any of these links don't work immediately, try again. The site seems to have a bunch of problems.
Of course, none of this is conclusive proof of Clinton's liberalism. But it is another piece of evidence that helps to disprove the idea that Clinton is a moderate, much less a conservative.