Lifetime ADA Voting Ratings
Sen. John Kerry................92
Rep. Dennis Kucinich........86
Sen. John Edwards..........85
Sen. Joseph Lieberman... 78

It's interesting to see that Edwards, generally thought of as significantly more centrist than Kerry (I called him a centrist myself in a recent posting), does not have a rating all that different from Kerry's, and that his is very close to that of Kucinich, generally considered to be very liberal. Not only that, but Lieberman, whom many liberals consider to be so conservative as to be "Bush Lite", lags not too far behind. For purposes of comparison, Zell Miller, who really is a Republican in all but name, had a a rating of 30% in 2002. (I couldn't find a current lifetime rating for him, or a more recent one, for that matter.)

Looking at other liberal organizations which offer ratings (these are all for 2003 and come from Vote Smart):

Friends Committee on National Legislation
Kerry 100 / Edwards 83 / Kucinich 78 / Lieberman 75

National Committee for an Effective Congress
Kerry 100 / Edwards 95 / Lieberman 95 / Kucinich 85

US Public Interest Research Group
Kucinich 100 / Kerry 95 / Edwards 81 / Lieberman 81

On the flip side there are the American Conservative Union's ratings:

ACU Lifetime Voting Ratings
Sen. John Kerry...............5
Sen. John Edwards........12
Rep Dennis Kucinich.......15
Sen. Joseph Lieberman..19

Once more, for comparison, Zell Miller gets a 65.

Here again we see the same pattern. Kerry is the least conservative of the four, but Edwards is not far behind, and here he's actually ahead of the "very liberal" Kucinich. The "Bush Lite" Lieberman is only a few points away from them, and they're all a long way away from Zell Miller.

BTW, and this is indicative of any awful lot that's been said about the weakness of liberal infrastructure compared to that of the right-wing, the ADA website is an absolute mess, a shambles that seems to be about 2 years out of date, while the website for the ACU is well-organized and up to date.

You can see a summary of other scorecards (for environmental issues, labor issues, civil rights issues etc.) here, or use Vote Smart to search for issue-oriented organization ratings.

Update: There is at least one liberal group which rates Kucinich muchhigher than the other candidates, and that's

Public Citizen's Congress Watch
Kucinich 100 / Edwards 45 / Lieberman 36 / Kerry 27

which is, not too surprisingly, just about in inverse order of their length of service in Congress.