Checking out the Web site, I came across a chart that rated all senators on an ideological scale. It takes the ratings of eight organizations that rates lawmakers’ voting records in their area during 2004 and 2005 and averages the scores from each organizations. These are:
ACLU – American Civil Liberties Union
ADA – Americans for Democratic Action
CDF – Children’s Defense Fund
LCV – League of Conservation Voters
NAACP – National Association for the Advancement of Colored People
NARAL – National Abortion and Reproductive Rights Action League
PTA – National Parent-Teacher Association
SEIU – Service Employees International Union

The resulting score rates senators from the most liberal (score: 100) to the least (score: 0). Conservative groups are clearly underrepresented here, but I found the distribution interesting nonetheless in reflecting the polarization of American politics and the disappearance of the middle:
21 of 45 Democratic senators averaged 90% or higher.
43 of 55 Republican senators averaged 9% or lower.

Only seven senators occupied the broad middle of the political spectrum, between 70% and 30%: Kent Conrad (D-ND), Lincoln Chafee (R-RI), Susan Collins (R-ME), Olympia Snowe (R-ME), Arlen Specter, R-PA), Ben Nelson (D-NE), and Mike DeWine (R-OH). Chafee and DeWine face tight reelection battles.

Kay Bailey Hutchison scored 9. John Cornyn scored 3. John McCain, said by some to be not conservative enough to win the Republican nomination for president, scored 17. Highest score for any state was Illinois, 196 (Barack Obama 98, Dick Durbin 98). Lowest score for any state was Kentucky, 4 (Mitch McConnell 3, Jim Bunning 1).